Most ancient creeds, including the Nicene, begin by declaring that we believe in one God, the Father Almighty. This is given as the first article of the Christian faith. The identification of the one God with the person of the Father in particular is not only easily proved from the scriptures, but is also extensively witnessed to by the ante-nicene and nicene church fathers. A non-comprehensive list of quotes showing this is given below.
“There is one body and one Spirit, just as also you were called in one hope of your calling; 5 one Lord, one faith, one baptism, 6 one God and Father of all who is over all and through all and in all.” Ephesians 4:4-6 NAS
“This is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent.” John 17:3 NAS
“yet for us there is but one God, the Father, from whom are all things and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him.” 1 Corinthians 8:6 NAS
Ancient Patristic Witness:
Clement of Rome:
“Why are there strifes, and tumults, and divisions, and schisms, and wars among you? Have we not [all] one God and one Christ? Is there not one Spirit of grace poured out upon us?” 1 Clement, Chapter XLVI.
Ignatius of Antioch:
“On this account also they were persecuted, being inspired by His grace to fully convince the unbelieving that there is one God, who has manifested Himself by Jesus Christ His Son, who is His eternal Word, not proceeding forth from silence, and who in all things pleased Him that sent Him.” Epistle to the Magnesians (shorter version), Chapter VIII.
“If any one confesses Christ Jesus the Lord, but denies the God of the law and of the prophets, saying that the Father of Christ is not the Maker of heaven and earth, he has not continued in the truth any more than his father the devil, and is a disciple of Simon Magus, not of the Holy Spirit. If any one says there is one God, and also confesses Christ Jesus, but thinks the Lord to be a mere man, and not the only-begotten God, and Wisdom, and the Word of God, and deems Him to consist merely of a soul and body, such an one is a serpent, that preaches deceit and error for the destruction of men.” Epistle to the Philadelphians (longer version), Chapter VI.
“The prophets also, when they speak as in the person of God, [saying,] “I am God, the first [of beings], and I am also the last, and besides Me there is no God,” concerning the Father of the universe, do also speak of our Lord Jesus Christ.” Epistle to the Antiochians, Chapter III.
“The Evangelists, too, when they declared that the one Father was “the only true God,” did not omit what concerned our Lord, but wrote: “In the beginning was the Word, and the Word was with God, and the Word was God.” Epistle to the Antiochians, Chapter IV.
“For if there is one God of the universe, the Father of Christ, “of whom are all things;” and one Lord Jesus Christ, our [Lord], “by whom are all things;” and also one Holy Spirit, who wrought in Moses, and in the prophets and apostles; and also one baptism, which is administered that we should have fellowship with the death of the Lord; and also one elect Church; there ought likewise to be but one faith in respect to Christ. For “there is one Lord, one faith, one baptism; one God and Father of all, who is through all, and in all.”” Epistle to the Philippians, Chapter I.
“There is then one God and Father, and not two or three; One who is; and there is no other besides Him, the only true [God]. For “the Lord thy God,” saith [the Scripture], “is one Lord.” And again, “Hath not one God created us? Have we not all one Father? And there is also one Son, God the Word. For “the only-begotten Son,” saith [the Scripture], “who is in the bosom of the Father.” And again, “One Lord Jesus Christ.” And in another place, “What is His name, or what His Son’s name, that we may know?” And there is also one Paraclete. For “there is also,” saith [the Scripture], “one Spirit,” since “we have been called in one hope of our calling.”” Epistle to the Philippians, Chapter II.
“Ignatius answered, “Thou art in error when thou callest the dæmons of the nations gods. For there is but one God, who made heaven, and earth, and the sea, and all that are in them; and one Jesus Christ, the only-begotten Son of God, whose kingdom may I enjoy.”” Ignatius before Trajan, at his martyrdom. From the Martyrdom of Ignatius, Chapter II.
Irenaeus of Lyons:
“And others of them, with great craftiness, adapted such parts of Scripture to their own figments, lead away captive from the truth those who do not retain a stedfast faith in one God, the Father Almighty, and in one Lord Jesus Christ, the Son of God.” Against Heresies, Book I. Chapter III. 6.
“The fallacy, then, of this exposition is manifest. For when John, proclaiming one God, the Almighty, and one Jesus Christ, the Only-begotten, by whom all things were made, declares that this was the Son of God, this the Only-begotten, this the Former of all things, this the true Light who enlighteneth every man, this the Creator of the world, this He that came to His own, this He that became flesh and dwelt among us,–these men, by a plausible kind of exposition, perverting these statements, maintain that there was another Monogenes, according to production, whom they also style Arche.” Against Heresies, Book I. Chapter IX. 2.
“But if the Word of the Father who descended is the same also that ascended, He, namely, the Only-begotten Son of the only God, who, according to the good pleasure of the Father, became flesh for the sake of men, the apostle certainly does not speak regarding any other, or concerning any Ogdoad, but respecting our Lord Jesus Christ.” Against Heresies, Book I. Cahpter IX. 3.
“The Church, though dispersed through our the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: [She believes] in one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit, who proclaimed through the prophets the dispensations of God” Against Heresies, Book I. Chapter X. 1.
“The rule of truth which we hold, is, that there is one God Almighty, who made all things by His Word, and fashioned and formed, out of that which had no existence, all things which exist. Thus saith the Scripture, to that effect: “By the Word of the Lord were the heavens established, and all the might of them, by the spirit of His mouth.” And again, “All things were made by Him, and without Him was nothing made.”” Against Heresies, Book I. Chapter XXII. 1.
“It is proper, then, that I should begin with the first and most important head, that is, God the Creator, who made the heaven and the earth, and all things that are therein (whom these men blasphemously style the fruit of a defect), and to demonstrate that there is nothing either above Him or after Him; nor that, influenced by any one, but of His own free will, He created all things, since He is the only God, the only Lord, the only Creator, the only Father, alone containing all things, and Himself commanding all things into existence.” Against Heresies, Book II. Chapter I. 1.
“Now, that this God is the Father of our Lord Jesus Christ, Paul the apostle also has declared, [saying,] “There is one God, the Father, who is above all, and through all things, and in us all.” I have indeed proved already that there is only one God; but I shall further demonstrate this from the apostles themselves, and from the discourses of the Lord. For what sort of conduct would it be, were we to forsake the utterances of the prophets, of the Lord, and of the apostles, that we might give heed to these persons, who speak not a word of sense?” Against Heresies, Book II. Chapter II. 5.
“That God is the Creator of the world is accepted even by those very persons who in many ways speak against Him, and yet acknowledge Him, styling Him the Creator, and an angel, not to mention that all the Scriptures call out [to the same effect], and the Lord teaches us of this Father who is in heaven, and no other, as I shall show in the sequel of this work. For the present, however, that proof which is derived from those who allege doctrines opposite to ours, is of itself sufficient,–all men, in fact, consenting to this truth: the ancients on their part preserving with special care, from the tradition of the first-formed man, this persuasion, while they celebrate the praises of one God, the Maker of heaven and earth; others, again, after them, being reminded of this fact by the prophets of God, while the very heathen learned it from creation itself. For even creation reveals Him who formed it, and the very work made suggests Him who made it, and the world manifests Him who ordered it. The Universal Church, moreover, through the whole world, has received this tradition from the apostles.” Against Heresies, Book II. Chapter IX, 1.
“But there is one only God, the Creator—He who is above every Principality, and Power, and Dominion, and Virtue: He is Father, He is God, He the Founder, He the Maker, He the Creator, who made those things by Himself, that is, through His Word and His Wisdom— heaven and earth, and the seas, and all things that are in them: He is just; He is good; He it is who formed man, who planted paradise, who made the world, who gave rise to the flood, who saved Noah; He is the God of Abraham, and the God of Isaac, and the God of Jacob, the God of the living: He it is whom the law proclaims, whom the prophets preach, whom Christ reveals, whom the apostles make known to us, and in whom the Church believes. He is the Father of our Lord Jesus Christ: through His Word, who is His Son, through Him He is revealed and manifested to all to whom He is revealed; for those [only] know Him to whom the Son has revealed Him. But the Son, eternally coexisting with the Father, from of old, yea, from the beginning, always reveals the Father to Angels, Archangels, Powers, Virtues, and all to whom He wills that God should be revealed.” Against Heresies, Book II. Chapter XXX. 9.
“Now, that the preaching of the apostles, the authoritative teaching of the Lord, the announcements of the prophets, the dictated utterances of the apostles, and the ministration of the law–all of which praise one and the same Being, the God and Father of all, and not many diverse beings, nor one deriving his substance from different gods or powers, but [declare] that all things [were formed] by one and the same Father (who nevertheless adapts [His works] to the natures and tendencies of the materials dealt with), things visible and invisible, and, in short, all things that have been made [were created] neither by angels, nor by any other power, but by God alone, the Father–are all in harmony with our statements, has, I think, been sufficiently proved, while by these weighty arguments it has been shown that there is but one God, the Maker of all things.” Against Heresies, Book II. Chapter XXXV. 4.
“These have all declared to us that there is one God, Creator of heaven and earth, announced by the law and the prophets; and one Christ the Son of God. If any one do not agree to these truths, he despises the companions of the Lord; nay more, he despises Christ Himself the Lord; yea, he despises the Father also, and stands self-condemned, resisting and opposing his own salvation, as is the case with all heretics.” Against Heresies, Book III. Chapter I. 2.
“In the time of this Clement, no small dissension having occurred among the brethren at Corinth, the Church in Rome despatched a most powerful letter to the Corinthians, exhorting them to peace, renewing their faith, and declaring the tradition which it had lately received from the apostles, proclaiming the one God, omnipotent, the Maker of heaven and earth, the Creator of man, who brought on the deluge, and called Abraham, who led the people from the land of Egypt, spake with Moses, set forth the law, sent the prophets, and who has prepared fire for the devil and his angels. From this document, whosoever chooses to do so, may learn that He, the Father of our Lord Jesus Christ, was preached by the Churches, and may also understand the apostolical tradition of the Church, since this Epistle is of older date than these men who are now propagating falsehood, and who conjure into existence another god beyond the Creator and the Maker of all existing things.” Against Heresies, Book III. Chapter III. 3.
“To which course many nations of those barbarians who believe in Christ do assent, having salvation written in their hearts by the Spirit, without paper or ink, and, carefully preserving the ancient tradition, believing in one God, the Creator of heaven and earth, and all things therein, by means of Christ Jesus, the Son of God; who, because of His surpassing love towards His creation, condescended to be born of the virgin, He Himself uniting man through Himself to God, and having suffered under Pontius Pilate, and rising again, and having been received up in splendour, shall come in glory, the Saviour of those who are saved, and the Judge of those who are judged, and sending into eternal fire those who transform the truth, and despise His Father and His advent.” Against Heresies, Book III. Chapter IV. 2.
“Since, therefore, this is sure and stedfast, that no other God or Lord was announced by the Spirit, except Him who, as God, rules over all, together with His Word, and those who receive the Spirit of adoption,  that is, those who believe in the one and true God, and in Jesus Christ the Son of God; and likewise that the apostles did of themselves term no one else as God, or name [no other] as Lord; and, what is much more important, [since it is true] that our Lord [acted likewise], who did also command us to confess no one as Father, except Him who is in the heavens, who is the one God and the one Father;–those things are clearly shown to be false which these deceivers and most perverse sophists advance” Against Heresies, Book IV, Chapter I. 1.
“And therefore it is right first of all to believe that there is One God, the Father, who made and fashioned all things, and made what was not that it should be, and who, containing all things, alone is uncontained.” The Demonstration of the Apostolic Preaching (TDAP)
“Thus then there is shown forth One God, the Father, not made, invisible, creator of all things; above whom there is no other God, and after whom there is no other God. And, since God is rational, therefore by (the) Word He created the things that were made; and God is Spirit, and by (the) Spirit He adorned all things…” TDAP
“This then is the order of the rule of our faith, and the foundation of the building, and the stability of our conversation: God, the Father, not made, not material, invisible; one God, the creator of all things: this is the first point of our faith. The second point is: The Word of God, Son of God, Christ Jesus our Lord, who was manifested to the prophets according to the form of their prophesying and according to the method of the dispensation of the Father: through whom all things were made; who also at the end of the times, to complete and gather up all things, was made man among men, visible and tangible, in order to abolish death and show forth life and produce a community of union between God and man. And the third point is: The Holy Spirit, through whom the prophets prophesied, and the fathers learned the things of God, and the righteous were led forth into the way of righteousness; and who in the end of the times was poured out in a new way upon mankind in all the earth, renewing man unto God.” TDAP
Theophilus of Antioch:
“But God at least, the Father and Creator of the universe, did not abandon mankind, but gave a law, and sent holy prophets to declare and teach the race of men, that each one of us might awake and understand that there is one God.” Theophilus to Autolycus, Book II. Chapter XXXIV.
Athenagoras of Athens:
“But, since our doctrine acknowledges one God, the Maker of this universe, who is Himself uncreated (for that which is does not come to be, but that which is not) but has made all things by the Logos which is from Him, we are treated unreasonably in both respects, in that we are both defamed and persecuted.” A Plea For the Christians, Chapter IV.
“That we are not atheists, therefore, seeing that we acknowledge one God, uncreated, eternal, invisible, impassible, incomprehensible, illimitable, who is apprehended by the understanding only and the reason, who is encompassed by light, and beauty, and spirit, and power ineffable, by whom the universe has been created through His Logos, and set in order, and is kept in being—I have sufficiently demonstrated. [I say “His Logos”], for we acknowledge also a Son of God.” A Plea For the Christians, Chapter X.
Clement of Alexandria:
““Now the just shall live by faith,” which is according to the covenant and the commandments; since these, which are two in name and time, given in accordance with the [divine] economy—being in power one—the old and the new, are dispensed through the Son by one God.” Stromata Book 2, Chapter VI
“Wherefore also the apostle designates as “the express image (χαρακτῆρα) of the glory of the Father” the Son, who taught the truth respecting God, and expressed the fact that the Almighty is the one and only God and Father, “whom no man knoweth but the Son, and he to whom the Son shall reveal Him. That God is one is intimated by those “who seek the face of the God of Jacob;” whom being the only God, our Saviour and God characterizes as the Good Father.” Stromata, Book 7, Chapter X.
“And that the men of highest repute among the Greeks knew God, not by positive knowledge, but by indirect expression,2407 Peter says in the Preaching: “Know then that there is one God, who made the beginning of all things, and holds the power of the end; and is the Invisible, who sees all things; incapable of being contained, who contains all things; needing nothing, whom all things need, and by whom they are; incomprehensible, everlasting, unmade, who made all things by the ‘Word of His power,’ that is, according to the gnostic scripture, His Son.”” Stromata Book 6, Chapter V
Tertullian of Carthage:
“The object of our worship is the One God, He who by His commanding word, His arranging wisdom, His mighty power, brought forth from nothing this entire mass of our world, with all its array of elements, bodies, spirits, for the glory of His majesty; whence also the Greeks have bestowed on it the name of Κόσμος. The eye cannot see Him, though He is (spiritually) visible.” Apology, Chapter XVII.
“We, however, as we indeed always have done (and more especially since we have been better instructed by the Paraclete, who leads men indeed into all truth), believe that there is one only God, but under the following dispensation, or οἰκονομία , as it is called, that this one only God has also a Son, His Word, who proceeded from Himself, by whom all things were made, and without whom nothing was made. Him we believe to have been sent by the Father into the Virgin, and to have been born of her—being both Man and God, the Son of Man and the Son of God, and to have been called by the name of Jesus Christ; we believe Him to have suffered, died, and been buried, according to the Scriptures, and, after He had been raised again by the Father and taken back to heaven, to be sitting at the right hand of the Father, and that He will come to judge the quick and the dead; who sent also from heaven from the Father, according to His own promise, the Holy Ghost, the Paraclete, the sanctifier of the faith of those who believe in the Father, and in the Son, and in the Holy Ghost.” Against Praxeas, Chapter II.
“Hence, therefore, their error becomes manifest; for, being ignorant that the entire order of the divine administration has from the very first had its course through the agency of the Son, they believe that the Father Himself was actually seen, and held converse with men, and worked, and was athirst, and suffered hunger (in spite of the prophet who says: “The everlasting God, the Lord, the Creator of the ends of the earth, shall never thirst at all, nor be hungry;” much more, shall neither die at any time, nor be buried!), and therefore that it was uniformly one God, even the Father, who at all times did Himself the things which were really done by Him through the agency of the Son” Against Praxeas, Chapter XVI.
“When, therefore, He attested His own unity, the Father took care of the Son’s interests, that Christ should not be supposed to have come from another God, but from Him who had already said, “I am God and there is none other beside me,” who shows us that He is the only God, but in company with His Son, with whom “He stretcheth out the heavens alone.”” Against Praxeas, Chapter XVIII.
“But, (this doctrine of yours bears a likeness) to the Jewish faith, of which this is the substance—so to believe in One God as to refuse to reckon the Son besides Him, and after the Son the Spirit.” Against Praxeas, Chapter XXXI.
“Him had the Law the People shown to be One God, whose mighty voice to Moses spake Upon the mount. Him this His Virtue, too, His Wisdom, Glory, Word, and Son, this Light 35 Begotten from the Light immense, proclaims Through the seers’ voices, to be One…” Five Books Against Marcion; Of Marcion’s Antithesis (Authorship Uncertain –found as an Appendix to Tertullian’s Writings)
“The particular points clearly delivered in the teaching of the apostles are as follow:– First, That there is one God, who created and arranged all things, and who, when nothing existed, called all things into being–God from the first creation and foundation of the world–the God of all just men, of Adam, Abel, Seth, Enos, Enoch, Noe, Sere, Abraham, Isaac, Jacob, the twelve patriarchs, Moses, and the prophets; and that this God in the last days, as He had announced beforehand by His prophets, sent our Lord Jesus Christ to call in the first place Israel to Himself, and in the second place the Gentiles, after the unfaithfulness of the people of Israel. This just and good God, the Father of our Lord Jesus Christ, Himself gave the law and the prophets, and the Gospels, being also the God of the apostles and of the Old and New Testaments.” De Principiis, Preface 4.
“But whether Orpheus, Parmenides, Empedocles, or even Homer himself, and Hesiod, are the persons whom he means by “inspired poets,” let any one show how those who follow their guidance walk in a better way, or lead a more excellent life, than those who, being taught in the school of Jesus Christ, have rejected all images and statues, and even all Jewish superstition, that they may look upward through the Word of God to the one God, who is the Father of the Word” Origen Against Celsus, Book VII. Chapter XLI.
“Accordingly, we worship with all our power the one God, and His only Son, the Word and the Image of God, by prayers and supplications; and we offer our petitions to the God of the universe through His only-begotten Son.” Origen Against Celsus, Book VIII. Chapter XIII.
Hippolytus of Rome:
“For it is right, in the first place, to expound the truth that the Father is one God, “of whom is every family,” “by whom are all things, of whom are all things, and we in Him.”” Against the Heresy of One Noetus, 3.
“If, therefore, all things are put under Him with the exception of Him who put them under Him, He is Lord of all, and the Father is Lord of Him, that in all there might be manifested one God, to whom all things are made subject together with Christ, to whom the Father hath made all things subject, with the exception of Himself. And this, indeed, is said by Christ Himself, as when in the Gospel He confessed Him to be His Father and His God. For He speaks thus: “I go to my Father and your Father, and to my God and your God.”” Against the Heresy of One Noetus, 6.
“Thus God the Father, the Founder and Creator of all things, who only knows no beginning, invisible, infinite, immortal, eternal, is one God; to whose greatness, or majesty, or power, I would not say nothing can be preferred, but nothing can be compared; of whom, when He willed it, the Son, the Word, was born, who is not received in the sound of the stricken air, or in the tone of voice forced from the lungs, but is acknowledged in the substance of the power put forth by God, the mysteries of whose sacred and divine nativity neither an apostle has learnt, nor prophet has discovered, nor angel has known, nor creature has apprehended.” A Treatise of Novatian Concerning the Trinity, Chapter XXXI.
“Assuredly God proceeding from God, causing a person second to the Father as being the Son, but not taking from the Father that characteristic that He is one God.” A Treatise of Novatian Concerning the Trinity, Chapter XXXI.
“But now, whatever He is, He is not of Himself, because He is not unborn; but He is of the Father, because He is begotten, whether as being the Word, whether as being the Power, or as being the Wisdom, or as being the Light, or as being the Son; and whatever of these He is, in that He is not from any other source, as we have already said before, than from the Father, owing His origin to His Father, He could not make a disagreement in the divinity by the number of two Gods, since He gathered His beginning by being born of Him who is one God.” A Treatise of Novatian Concerning the Trinity, Chapter XXXI.
“Thus making Himself obedient to His Father in all things, although He also is God, yet He shows the one God the Father by His obedience, from whom also He drew His beginning.” A Treatise of Novatian Concerning the Trinity, Chapter XXXI.
“The true and eternal Father is manifested as the one God, from whom alone this power of divinity is sent forth, and also given and directed upon the Son, and is again returned by the communion of substance to the Father. God indeed is shown as the Son, to whom the divinity is beheld to be given and extended. And still, nevertheless, the Father is proved to be one God; while by degrees in reciprocal transfer that majesty and divinity are again returned and reflected as sent by the Son Himself to the Father, who had given them; so that reasonably God the Father is God of all, and the source also of His Son Himself whom He begot as Lord.” A Treatise of Novatian Concerning the Trinity, Chapter XXXI.
“There is one God, the Father of the living Word, who is His subsistent Wisdom and Power and Eternal Image: perfect Begetter of the perfect Begotten, Father of the only-begotten Son.” A Declaration of Faith
“I have, as I think, sufficiently taught by arguments, and confirmed by witnesses, that which is sufficiently plain by itself, that there is one only King of the universe, one Father, one God.” The Divine Institutes, Chapter VII.
“But we, who are the children of God and the sons of peace, do preach the holy and right word of piety, and declare one only God, the Lord of the law and of the prophets, the Maker of the world, the Father of Christ; not a being that caused Himself, or begat Himself, as they suppose, but eternal, and without original, and inhabiting light inaccessible; not two or three, or manifold, but eternally one only; not a being that cannot be known or spoken of, but who was preached by the law and the prophets; the Almighty, the Supreme Governor of all things, the All-powerful Being; the God and Father of the Only-begotten, and of the First-born of the whole creation; one God, the Father of one Son” Apostolic Constitutions, Book VI. Section III.
“…we declare unto you, that there is only one God Almighty, besides whom there is no other, and that you must worship and adore Him alone, through Jesus Christ our Lord, in the most holy Spirit;” Apostolic Constitutions, Book VI. Section III.
“Nay I would add, that they were said even in anticipation of the folly of these Christ-opposers, that they might know, that whatsoever god they devise external to the Father’s Essence, he is not True God, nor Image and Son of the Only and First.” Against the Arians, Discourse III.
“He it is who through His Word made all things small and great, and we may not divide the creation, and says this is the Father’s, and this the Son’s, but they are of one God, who uses His proper Word as a Hand, and in Him does all things. This God Himself shews us, when He says, ‘All these things hath My Hand made;’ while Paul taught us as he had learned, that ‘There is one God, from whom all things; and one Lord Jesus Christ, through whom all things.” Defense of the Nicene Definition, Chapter III.
”But if this is not to be seen, but while the creatures are many, the Word is one, any one will collect from this, that the Son differs from all, and is not on a level with the creatures, but proper to the Father. Hence there are not many Words, but one only Word of the one Father, and one Image of the one God.” Against the Arians, Discourse II.
“For where at all have they found in divine Scripture, or from whom have they heard, that there is another Word and another Wisdom besides this Son, that they should frame to themselves such a doctrine? True, indeed, it is written, ‘Are not My words like fire, and like a hammer that breaketh the rock in pieces?’ and in the Proverbs, ‘I will make known My words unto you;’ but these are precepts and commands, which God has spoken to the saints through His proper and only true Word, concerning which the Psalmist said, ‘I have refrained my feet from every evil way, that I may keep Thy words.’ Such words accordingly the Saviour signifies to be distinct from Himself, when He says in His own person, ‘The words which I have spoken unto you.’ For certainly such words are not offsprings or sons, nor are there so many words that frame the world, nor so many images of the One God, nor so many who have become men for us, nor as if from many such there were one who has become flesh, as John says; but as being the only Word of God was He preached by John, ‘The Word was made flesh,’ and ‘all things were made by Him.’” Against the Arians, Discourse II.
“Accordingly when the Father is called the only God, and we read that there is one God, and ‘I am,’ and ‘beside Me there is no God,’ and ‘I the first and I the last,’ this has a fit meaning. For God is One and Only and First; but this is not said to the denial of the Son, perish the thought; for He is in that One, and First and Only, as being of that One and Only and First the Only Word and Wisdom and Radiance. And He too is the First, as the Fulness of the Godhead of the First and Only, being whole and full God.” Against the Arians, Discourse III.
“For, as the illustration shows, we do not introduce three Origins or three Fathers, as the followers of Marcion and Manichæus; since we have not suggested the image of three suns, but sun and radiance. And one is the light from the sun in the radiance; and so we know of but one origin; and the All-framing Word we profess to have no other manner of godhead, than that of the Only God, because He is born from Him.” Against the Arians, Discourse III.
“For there is but one form of Godhead, which is also in the Word; and one God, the Father, existing by Himself according as He is above all, and appearing in the Son according as He pervades all things, and in the Spirit according as in Him He acts in all things through the Word.” Against the Arians, Discourse III.
“For there is One God, and not many, and One is His Word, and not many; for the Word is God, and He alone has the Form of the Father.” Against the Arians, Discourse III.
“For the Word, being Son of the One God, is referred to Him of whom also He is; so that Father and Son are two, yet the Monad of the Godhead is indivisible and inseparable. And thus too we preserve One Beginning of Godhead and not two Beginnings, whence there is strictly a Monarchy” Against the Arians, Discourse IV.
“For the one God makes and creates; but Him He begets from Himself, Word or Wisdom.” Against the Arians, Discourse IV.
“The Triad, then, although the Word took a body from Mary, is a Triad, being inaccessible to addition or diminution; but it is always perfect, and in the Triad one Godhead is recognised, and so in the Church one God is preached, the Father of the Word.” To Epictetus
“The Father does all things, by the Word, and in the Holy Spirit: And so the Unity of the Holy Trinity is preserved: And so one God is preached in the Church; even He who is over all, and through all, and in all: Over all, as he is the Father and Original and Fountain of all; Through all by His Word; and in all, by His Holy Spirit.” Epistle Ad Serapion 1.
Cyril of Jerusalem:
“Further, do thou neither separate the Son from the Father, nor by making a con- fusion believe in a Son-Fatherhood; but believe that of One God there is One Only-begotten Son, who is before all ages God the Word; not the uttered word diffused into the air, nor to be likened to impersonal words; but the Word the Son, Maker of all who partake of reason, the Word who heareth the Father, and Himself speaketh.” On the Ten Points of Doctrine (Lecture IV)
“For there is One God, the Father of Christ; and One Lord Jesus Christ, the Only-begotten Son of the Only God; and One Holy Ghost…” On the Ten Points of Doctrine (Lecture IV)
“Of God as the sole Principle we have said enough to you yesterday: by “enough” I mean, not what is worthy of the subject, (for to reach that is utterly impossible to mortal nature), but as much as was granted to our infirmity. I traversed also the bye-paths of the manifold error of the godless heretics: but now let us shake off their foul and soul-poisoning doctrine, and remembering what relates to them, not to our own hurt, but to our greater detestation of them, let us come back to ourselves, and receive the saving doctrines of the true Faith, connecting the dignity of Fatherhood with that of the Unity, and believing In One God the Father: for we must not only believe in one God; but this also let us devoutly receive, that He is the Father of the Only-begotten, our Lord Jesus Christ.” The Father (Lecture VII)
“For thus shall we raise our thoughts higher than the Jews, who admit indeed by their doctrines that there is One God, (for what if they often denied even this by their idolatries?); but that He is also the Father of our Lord Jesus Christ, they admit not; being of a contrary mind to their own Prophets, who in the Divine Scriptures affirm, The Lord said unto me, Thou art My Son, this day have I begotten thee.” The Father (Lecture VII)
“But let us adopt the godly doctrine of our Faith, worshipping one God the Father of the Christ…” The Father (Lecture VII)
“For if a Father, He is certainly the Father of a Son; and if a Son, certainly the Son of a Father. Lest therefore from our speaking thus, In One God, the Father Almighty, Maker of Heaven and Earth, and of All Things Visible and Invisible, and from our then adding this also, And in One Lord Jesus Christ, any one should irreverently suppose that the Only-begotten is second in rank to heaven and earth,—for this reason before naming them we named God the Father, that in thinking of the Father we might at the same time think also of the Son: for between the Son and the Father no being whatever comes.” The Father (Lecture VII)
“But worship thou One God the Almighty, the Father of our Lord Jesus Christ.” Almighty (Lecture VIII)
“Be not thou carried away with the Jews when they craftily say, There is one God alone; but with the knowledge that God is One, know that there is also an Only-begotten Son of God.” On the Clause, And In One Lord Jesus Christ, with a Reading From the First Epistle to the Corinthians (Lecture X)
“There is One God, the Father, Lord of the Old and of the New Testament: and One Lord, Jesus Christ, who was prophesied of in the Old Testament, and came in the New; and One Holy Ghost, who through the Prophets preached of Christ, and when Christ was come, descended, and manifested Him.” On the Article, And In One Holy Ghost, the Comforter, Which Spake In the Prophets (Lecture XVI)
“The Father through the Son, with the Holy Ghost, is the giver of all grace; the gifts of the Father are none other than those of the Son, and those of the Holy Ghost; for there is one Salvation, one Power, one Faith; One God, the Father; One Lord, His only-begotten Son; One Holy Ghost, the Comforter. ” On the Article, And In One Holy Ghost, the Comforter, Which Spake In the Prophets (Lecture XVI)
“I believe that there is one God the Father who has received life from no one and that there is one Son who has received from the Father his being and his life so that he exists and that there is one Holy Spirit, the Paraclete, who enlightens and sanctifies our souls. I state this on the basis of the scriptures.” (Debate With Augustine)
“We worship one God, unborn, unmade, invisible, who has not come down to human contacts and human flesh. The Son is not a small, but a great God, as blessed Paul says, Awaiting the blessed hope and coming of the glory of the great God and our Savior Jesus Christ (Ti 2:13). This great God, Christ, says, I ascend to my Father and your Father, to my God and your God (Jn 20:17). By his own subjection he acknowledged that there is one God. This is the one God, then, as we have already shown by testimonies, whom Christ and the Holy Spirit adore and every creature venerates and worships. This is the reason we profess one God. It is not that a union or mixture of the Son with the Father—and certainly not a union or mixture of the Holy Spirit with the Father and the Son—makes one God. Rather, he alone is the one perfect God who, as you go on to say, received life from no one and who granted to the Son his revelation, that he has life in himself. We say they are united in charity and in harmony.” (Debate With Augustine)
“In accord with the testimonies that I have produced, I say that the Father alone is the one God, not one along with a second and a third, but that he alone is the one God. If he alone is not the one God, he is a part.” (Debate With Augustine)