Scripture is clear in teaching that the one God is the person of the Father in particular, as can be observed as explicitly taught in the following passages:
“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 4:4-5 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)
Yet scripture is also clear in teaching that the one God has a Son, and His Holy Spirit, who are each distinct persons from the Father, and each of the same divine nature as He. This easily raises the question, ‘how can the Son and Holy Spirit both be God, having the same divinity as the Father, Who is the one God, without constituting second and third Gods?’
The answer to this question is multifaceted: the Father is the one God because He alone is the Supreme Cause, or uncaused Cause, and He alone is the Supreme Authority, or Head without a head, as we have observed in the last two installments of this series. Additionally, we may point to the unity of the Son and Spirit with the Father in respect to both their divine nature and their relationship to Him as reasons why They cannot be said to constitute second and third Gods. In this installment, we will examine how the unity of the divine nature does not allow the Son and Spirit to constitute second and third Gods.
Firstly, let us observe that the unity of the divine nature is not the cause of there being only one God- rather, it is a result of it; as such, if there were a plurality of divine natures, it would create a plurality of Gods due to their know being multiple species of divinity. So when we bring up the unity of the divine nature in defending the unity of God, we aren’t saying that there is only one God because there is only one divine nature, but rather that the Son and Spirit’s divinity cannot infringe upon the unity of God because They are not of different divine natures than the Father, but have the Father’s own divine nature.
If we were to argue, as some have tried to, that the sole or primary reason that there is only one God because there is only one divine nature, one might easily reply that in the case of men there is but one human nature common to many men, yet there are many men, not one man, because there are many human persons; so also, such a person could argue, simply having three divine persons all share a common divine nature does not make Them constitute one God, but three Gods. This line of argumentation is valid, if all we can point to in order to assert that there is one God is that the Father, Son, and Spirit share a common divinity as any three individuals in creation may share a common species.
But as we have observed in the last two installments of this series, the scriptures do not teach that there is only one God because there is only one divine nature, but because the Father, Who alone is the Supreme Cause of all and Supreme Authority over all, is one. Thus there is only one God, although there are three divine persons, because there is one Supreme Cause and Authority, the person of the Father. This, we observed, is why scripture styles God the Father in particular the “one God”, even while teaching the divinity of the persons of the Son and Holy Spirit.
And yet, it is important to note that the divinity of the Son and Spirit is identical to that of the Father; there are not three different divine natures, but one divine nature. Thus no one can charge Christians with tritheism on account of the Son or Spirit introducing a second or third divinity; rather, as the Son and Spirit are from the Father as Their Origin and Source by eternal generation and procession, They have communicated to Them in an ineffable way the divine nature of the only true God, the Father.
Thus scripture ascribes to the Son all the same divine attributes it ascribes to the Father, excepting fatherhood, and Supreme Headship, and being unoriginate, since those attributes of the Father are incommunicable. Similarly, we see the scriptures ascribe divine attributes to the Holy Spirit. Scripture also outright calls the Son “God” in John 1:1, which may rightly be viewed as referring to the Son’s divinity. Colossians 2:9 also tells us that Christ has the “fullness of deity”. The many references to and implications of the Son and Spirit’s divinity in scripture are themselves enough to prove that Their divinity is the same as that of the Father simply by way of necessary logical deduction from the fact that while the Son and Spirit are divine, They do not constitute second and third Gods, for there is only one God, the Father. In order for the Son and Spirit to not constitute second and third Gods They must have exactly the same divine nature as the Father, or else, as we mentioned above, a plurality of Gods would be introduced by way of a plurality of divine natures.
But we can also see the Son and Spirit’s exactly identical divinity from scripture’s teaching that the Son is begotten of the Father, and that the Spirit proceeds from Him as His Spirit. It is impious to think that the very Spirit of God would be anything other than divine, of the same divine nature as the one true God whose Holy Spirit He is. Likewise, it is absurd to suggest that God did not beget a Son who is of the same divine nature as He. God’s eternal fatherhood of His only-begotten Son is the very pattern off of which all human and created fatherhood is modeled. And in human fatherhood, a man’s son is always of the same nature as the father who begat him. So it is with all animals, that each begets after its own kind, there being an exact identicality of nature between the one begotten and the begetter. Thus every human son has the humanity of His Father. So also, the Lord Jesus Christ, the being the only begotten Son of the only true God, has the divinity of His Father, being of one and the same divine nature with the one true God Who begat Him before the ages. For a more detailed demonstration of eternal generation from the holy scriptures, see Eternal Generation Proved from the Scriptures.
Thus we see that the Son and Spirit, being of the same divine nature as the Father Whose Son and Spirit They are, do not create a plurality of Gods on account of a plurality of divine natures; but of one God, the Father, are one only-begotten Son and one Holy Spirit, who have the very same divine nature as the one God Whose Son and Spirit They are.
In addition to the proofs cited from scripture, we may bring to bear the testimony of many church fathers; not that the testimony of any man or council is sufficient to prove any point of doctrine true, but these are witnesses to which the truths which are known with certainty from the scriptures alone:
Novatian of Rome
“For all things being subjected to Him as the Son by the Father, while He Himself, with those things which are subjected to Him, is subjected to His Father, He is indeed proved to be Son of His Father; but He is found to be both Lord and God of all else. Whence, while all things put under Him are delivered to Him who is God, and all things are subjected to Him, the Son refers all that He has received to the Father, remits again to the Father the whole authority of His divinity. 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. Moreover, the Son is God of all else, because God the Father put before all Him whom He begot. Thus the Mediator of God and men, Christ Jesus, having the power of every creature subjected to Him by His own Father, inasmuch as He is God; with every creature subdued to Him, found at one with His Father God, has, by abiding in that condition that He moreover was heard, briefly proved God His Father to be one and only and true God.” (On the Trinity, Chapter 31)
“The children of the Jews first received the confession of the one God in opposition to the polytheistic error of the Greeks. But the saving grace of recognizing that the same [God] is also Father of an only-begotten Son has been given to the Church as a special privilege. For as Son it knows Jesus Christ alone and no other, not according to generation of the flesh that he assumed (for it has been taught to call this flesh the “form of a slave” and “Son of Man”), but according to his [generation] before all ages from God himself and the Father, [which is] unknowable to all. According to this [generation from God] the fullness of the paternal divinity also made him, the Son, God, and so as a result he possesses a divinity that is not his own, [not] one separated from that of the Father, nor one that is without source and that is unbegotten, nor one that is foreign, from somewhere else, and different from the Father’s. Rather, he is filled with divinity by participating in the paternal [divinity] itself, which pours into him as from a fountain. For the great Apostle taught that “in him alone dwells the fulness” of the paternal “divinity.” For this reason then, one God is proclaimed by the Church of God, “and there is no other beside him,” but also one only-begotten Son of God, the image of the paternal divinity, who, because of this, is God.” (On Ecclesiastical Theology, Book I, Ch 2)
“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.)
“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)
Hilary of Poitiers
“And if any one hearing that the Only-begotten Son is like the invisible God, denies that the Son who is the image of the invisible God (whose image is understood to include essence) is Son in essence, as though denying His true Sonship: let him be anathema.
15. It is here insisted that the nature is indistinguishable and entirely similar. For since He is the Only-begotten Son of God and the image of the invisible God, it is necessary that He should be of an essence similar in species and nature. Or what distinction can be made between Father and Son affecting their nature with its similar genus, when the Son subsisting through the nature begotten in Him is invested with the properties of the Father, viz., glory, worth, power, invisibility, essence? And while these prerogatives of divinity are equal we neither understand the one to be less because He is Son, nor the other to be greater because He is Father; since the Son is the image of the Father in species, and not dissimilar in genus; since the similarity of a Son begotten of the substance of His Father does not admit of any diversity of substance, and the Son and image of the invisible God embraces in Himself the whole form of His Father’s divinity both in kind and in amount: and this is to be truly Son, to reflect the truth of the Father’s form by the perfect likeness of the nature imaged in Himself.” (De Synodis)
“VIII. And if any one understanding that the Son is like in essence to Him whose Son He is admitted to be, says that the Son is the same as the Father, or part of the Father, or that it is through an emanation or any such passion as is necessary for the procreation of corporeal children that the incorporeal Son draws His life from the incorporeal Father: let him be anathema.
21. We have always to beware of the vices of particular perversions, and countenance no opportunity for delusion. For many heretics say that the Son is like the Father in divinity in order to support the theory that in virtue of this similarity the Son is the same Person as the Father: for this undivided similarity appears to countenance a belief in a single monad. For what does not differ in kind seems to retain identity of nature.
22. But birth does not countenance this vain imagination; for such identity without differentiation excludes birth. For what is born has a father who caused its birth. Nor because the divinity of Him who is being born is inseparable from that of Him who begets, are the Begetter and the Begotten the same Person; while on the other hand He who is born and He who begets cannot be unlike.” (De Synodis)
Cyril of Jerusalem
“We believe then In the Only-Begotten Son of God, Who Was Begotten of the Father Very God. For the True God begets not a false god, as we have said, nor did He deliberate and afterwards beget ; but He begot eternally, and much more swiftly than our words or thoughts: for we speaking in time, consume time; but in the case of the Divine Power, the generation is timeless. And as I have often said, He did not bring forth the Son from non-existence into being, nor take the non-existent into sonship : but the Father, being Eternal, eternally and ineffably begot One Only Son, who has no brother. Nor are there two first principles; but the Father is the head of the Son 1 Corinthians 11:3; the beginning is One. For the Father begot the Son Very God, called Emmanuel; and Emmanuel being interpreted is, God with us Matthew 1:23 .” (Catechetical Lecture 11)
“For the Father being Very God begot the Son like Himself, Very God…” (Catechetical Lecture 11)
“I shall give you another testimony, my friends, from the Scriptures, that God begot before all creatures a Beginning, [who was] a certain rational power [proceeding] from Himself, who is called by the Holy Spirit, now the Glory of the Lord, now the Son, again Wisdom, again an Angel, then God, and then Lord and Logos; and on another occasion He calls Himself Captain, when He appeared in human form to Joshua the son of Nave (Nun). For He can be called by all those names, since He ministers to the Father’s will, and since He was begotten of the Father by an act of will; just as we see happening among ourselves: for when we give out some word, we beget the word; yet not by abscission, so as to lessen the word [which remains] in us, when we give it out: and just as we see also happening in the case of a fire, which is not lessened when it has kindled [another], but remains the same; and that which has been kindled by it likewise appears to exist by itself, not diminishing that from which it was kindled [It must be noted that in the examples he gives, Justin assumes the identicality of the nature of the Word to the Father in respect to His divinity, as a word expressed is in essence identical to the internal idea expressed, and one fire kindled of another is of no other nature than the fire from which it is kindled. So also, the Son begotten of the Father is of no other nature than that of the Father Himself, having the same divine nature as He.]. The Word of Wisdom, who is Himself this God begotten of the Father of all things, and Word, and Wisdom, and Power, and the Glory of the Begetter, will bear evidence to me, when He speaks by Solomon the following…” (Dialogue With Trypho, Chapter 61)
“And that this power which the prophetic word calls God, as has been also amply demonstrated, and Angel, is not numbered [as different] in name only like the light of the sun but is indeed something numerically distinct, I have discussed briefly in what has gone before; when I asserted that this power was begotten from the Father, by His power and will, but not by abscission, as if the essence of the Father were divided; as all other things partitioned and divided are not the same after as before they were divided: and, for the sake of example, I took the case of fires kindled from a fire, which we see to be distinct from it, and yet that from which many can be kindled is by no means made less, but remains the same.” (Dialogue With Trypho, Chapter 128)
Quotes from Eusebius taken from: Eusebius Pamphilius, On Ecclesiastical Theology, trans. Kelly McCarthy Sproerl and Markus Vinzent (Washington, D.C.: The Catholic University of America Press, 2017).