“We believe in one God the Father Almighty, the Creator and Maker of all things, from whom all fatherhood in heaven and on earth is named.
And in His Only-begotten Son our Lord Jesus Christ, who before all ages was begotten from the Father, God from God, Light from Light, by whom all things were made, in heaven and one the earth, visible and invisible, being Word and Wisdom and Power and Life and True Light, who in the last days was made man for us, and was born of the Holy Virgin, crucified and died and was buried, and rose again from the dead on the third day, and was taken up into heaven, and sat down on the right hand of the Father, and is coming at the consummation of the age to judge the living and the dead, and to render to everyone according to his works; whose kingdom endured unceasingly unto all the ages; for He sits on the right hand of the Father, not only in this age, but also in that which is to come.
And we believe in the Holy Ghost, that is, the Paraclete, which, having promised to the apostles, He sent forth after the ascension into heaven, to teach them and to remind of all things; through whom also shall be sanctified the souls of those who sincerely believe in Him.
But those who say that the Son was from nothing, or from other subsistence and not from God; and that there was a time or age when He was not, the catholic and holy church regards as aliens. Likewise those who say that there are three Gods, or that Christ is not God, or that before the ages He was neither Christ nor Son of God, or that Father and Son or Holy Ghost are the same, or that the Son is ingenerate, or that the Father begat the Son not by choice or will: the holy and catholic church anathematizes.
1. For neither is it safe to say that the Son is from nothing, (since this is no where spoken of Him in divinely inspired Scripture,) nor again of any other subsistence before existing beside the Father, but from God alone do we define Him genuinely to be generated. For the divine Word teaches that the Ingenerate and Unbegone, the Father of Christ, is One.
2. Nor may we, adopting the hazardous position, ‘There was once when He was not,’ from unscriptural sources, imagine any interval of time before Him, but only the God who has generated Him apart from time; for through Him both times and ages came to be. Yet we must not consider the Son to be co-unbegun and co-ingenerate with the Father; for no one can be properly called Father or Son of one who is co-unbegun and co-ingenerate with Him. But we acknowledge that the Father who alone is unbegun and ingenerate, has generated inconceivably and incomprehensibly to all; and that the Son has been generated before ages, and in no wise to be ingenerate Himself like the Father, but to have the Father who generated Him as His beginning; for ‘the head of Christ is God’ (1 Corinthians 11:3).
3. Nor again, in confessing three realities and three persons, of the Father and the Son and the Holy Ghost according to the Scriptures, do we therefore make Gods three; since we acknowledge the self-complete and ingenerate and unbegun and invisible God to be one only, the God and Father (John 20:17) of the Only-begotten, who alone has being from Himself, and alone vouchsafes this to all others bountifully.
4. Nor again, in saying that the Father of our Lord Jesus Christ is one only God, the only ingenerate, do we therefore deny that Christ also is God before ages; as the disciples of Paul of Samosata, who say that after the incarnation He was by advance made God, from being made by nature a mere man. For we acknowledge, that though He be subordinate to His Father and God, yet, being before ages begotten of God, He is God perfect according to nature and true, and not first man and then God, but first God and then becoming man for us, and never having been deprived of being.
5. We abhor besides, and anathematize those who make a pretence of saying that He is but the mere word of God and unexisting, having His being in another – now as if pronounced, as some speak, now as mental – holding that He was not Christ or Son of God or mediator or image of God before ages; but that He first became Christ and Son of God, when He took our flesh from the virgin, not quite four hundred years ago. For they will have it that then Christ began His kingdom, and that it will have an end after the consummation of all and the judgment. Such are the disciples of Marcellus and Scotinus of Galatian Ancyra, who, equally with Jews, rejected Christ’s existence before ages, and His Godhead, and unending kingdom, upon pretence of supporting the divine monarchy. We, on the contrary, regard Him not as simply God’s pronounced word or self, and Son of God and Christ, being and abiding with His Father before ages, and that not in foreknowledge only, and ministering to Him for the whole framing whether of things visible or invisible. For it is He to whom the Father said, ‘Let us make man in our image, after our likeness’ (Genesis 1:26), who also was seen in His own person by the patriarchs, gave the law, was spoken by the prophets, and at last became man and manifested His own Father to all men, and reigns to never-ending ages. For Christ has taken no recent dignity, but we have believed Him to be perfect from the first and like in all things to the Father.
6. And those who say that the Father and Son and Holy Ghost are the same, and irreligiously take the three names of one and the same reality and person, we justly proscribe from the Church, because they suppose the illimitable and impassible Father to be also limitable and passable through His becoming man. For such are they whom Romans call Patripassians, and we Sabellians. For we acknowledge that the unchangeable Godhead and that Christ who was sent fulfilled the economy of the Incarnation.
7. And at the same time those who irreverently say that the Son has been generated not by choice or will, thus encompassing God with a necessity which excludes choice and purpose, so that He begat the Son unwillingly, we account as most irreligious and alien to the Church; in that they have dared to define such things concerning God, beside the common notions concerning Him, so, beside the intention of divinely inspired Scripture. For we, knowing that God is absolute and sovereign over Himself, have a religious judgment that He generated the Son voluntarily and freely. Yet, as we have a reverent belief in the Son’s words concerning Himself (Proverbs 8:22), ‘The Lord created me a beginning of His ways for His works,’ we do not understand Him to have been originated like the creatures or works which through Him came to be. For it is irreligious and alien to the ecclesiastical faith, to compare the Creator with handiworks created by Him, and to think that He has the same manner of origination with the rest. For divine Scripture teaches us assuredly and truly that the Only-begotten Son was generated sole and solely. Yet, in saying that the Son is in Himself, and both lives and exists like the Father, we do not on that account separate Him from the Father, imagining place and interval between their union in the way of bodies. For we believe that they are united with each other without mediation or distance, and that they exist inseparably. All the Father encompassing the Son, and all the Son hanging and adhering to the Father, and alone resting on the Father’s breast continually. Believing then in the all-perfect triad, the most holy, that is, in the Father, and the Son, and the Holy Ghost, and calling the Father God, and the Son God, yet we confess in them, not two Gods, but one dignity of Godhead, and one exact harmony of dominion, the Father alone being head over the whole universe wholly, and over the Son Himself, and the Son subordinated to the Father; but, excepting Him, ruling over all things after Him which through Himself have come to be, and granting the grace of the Holy Ghost unsparingly to the saints at the Father’s will. For that such is the account of the Divine Monarchy towards Christ, the sacred oracles have delivered to us.
Thus much, in addition to the faith before published in epitome, we have been compelled to draw forth at length, not in any officious display, but to clear away all unjust suspicion concerning our opinions among those who are ignorant of our affairs; and that all in the West may know, both the audacity of the slanders of the heterodox, and as to the Orientals, their ecclesiastical mind in the Lord, to which the divinely inspired Scriptures bear witness without violence, where men are not perverse.”
The above is simply one of the best statements of biblical trinitarianism we have from the early church. The heresies of Arianism, Modalism, and Tritheism are all excluded and denied, and classical trinitarianism, as was believed by the Ante-nicene church and is taught by the scriptures, is explained and defended amid the raging theological controversies and ecclesiastical and political power struggles of the fourth-century.
The Father is identified as the one God, Who alone is the supreme uncaused Cause of all, not only of all creation, but also of His own Son, as the Son was begotten of Him before all time, and of His own Spirit, as the Holy Spirit eternally proceeds from Him (see Why There is Only One God: One Supreme Cause). The Father likewise is alone the Supreme Authority over all, not only exercising headship over all creation, but also even over His own divine Son and Holy Spirit, Who eternally share the same divine nature as He (see Why There is Only One God: Headship and Why There is Only One God: One Divine Nature). The inseparability of the persons of the Trinity is also noted (see Why There is Only One God: Relational Unity).