Subject Continued. Third proof of the Son's eternity, viz. from other titles indicative of His coessentiality; as the Creator; One of the Blessed Trinity; as Wisdom; as Word; as Image. If the Son is a perfect Image of the Father, why is He not a Father also? Because God, being perfect, is not the origin of a race. Only the Father a Father because the Only Father, only the Son a Son because the Only Son. Men are not really fathers and really sons, but shadows of the True. The Son does not become a Father, because He has received from the Father to be immutable and ever the same
17 This is of itself a sufficient refutation of the Arian heresy; however, its heterodoxy will appear also from the following:— If God be Maker and Creator, and create His works through the Son, and we cannot regard things which come to be, except as being through the Word, is it not blasphemous, God being Maker, to say, that His Framing Word and His Wisdom once was not? It is the same as saying, that God is not Maker, if He had not His proper Framing Word which is from Him, but that that by which He frames, accrues to Him from without, and is alien from Him, and unlike in essence. Next, let them tell us this—or rather learn from it how irreligious they are in saying, 'Once He was not,' and, 'He was not before His generation;'— for if the Word is not with the Father from everlasting, the Triad is not everlasting; but a Monad was first, and afterwards by addition it became a Triad; and so as time went on, it seems what we know concerning God grew and took shape. And further, if the Son is not proper offspring of the Father's essence, but of nothing has come to be, then of nothing the Triad consists, and once there was not a Triad, but a Monad; and a Triad once with deficiency, and then complete; deficient, before the Son was originated, complete when He had come to be; and henceforth a thing originated is reckoned with the Creator, and what once was not has divine worship and glory with Him who was ever. Nay, what is more serious still, the Triad is discovered to be unlike Itself, consisting of strange and alien natures and essences. And this, in other words, is saying, that the Triad has an originated consistence. What sort of a religion then is this, which is not even like itself, but is in process of completion as time goes on, and is now not thus, and then again thus? For probably it will receive some fresh accession, and so on without limit, since at first and at starting it took its consistence by way of accessions. And so undoubtedly it may decrease on the contrary, for what is added plainly admits of being subtracted.
18. But this is not so: perish the thought; the Triad is not originated; but there is an eternal and one Godhead in a Triad, and there is one Glory of the Holy Triad. And you presume to divide it into different natures; the Father being eternal, yet you say of the Word which is seated by Him, 'Once He was not;' and, whereas the Son is seated by the Father, yet you think to place Him far from Him. The Triad is Creator and Framer, and you fear not to degrade It to things which are from nothing; you scruple not to equal servile beings to the nobility of the Triad, and to rank the King, the Lord of Sabaoth with subjects. Cease this confusion of things unassociable, or rather of things which are not with Him who is. Such statements do not glorify and honour the Lord, but the reverse; for he who dishonours the Son, dishonours also the Father. For if the doctrine of God is now perfect in a Triad, and this is the true and only Religion, and this is the good and the truth, it must have been always so, unless the good and the truth be something that came after, and the doctrine of God is completed by additions. I say, it must have been eternally so; but if not eternally, not so at present either, but at present so, as you suppose it was from the beginning—I mean, not a Triad now. But such heretics no Christian would bear; it belongs to Greeks, to introduce an originated Triad, and to level It with things originate; for these do admit of deficiencies and additions; but the faith of Christians acknowledges the blessed Triad as unalterable and perfect and ever what It was, neither adding to It what is more, nor imputing to It any loss (for both ideas are irreligious), and therefore it dissociates It from all things generated, and it guards as indivisible and worships the unity of the Godhead Itself; and shuns the Arian blasphemies, and confesses and acknowledges that the Son was ever; for He is eternal, as is the Father, of whom He is the Eternal Word,— to which subject let us now return again.
19. If God be, and be called, the Fountain of wisdom and life— as He says by Jeremiah, 'They have forsaken Me the Fountain of living waters;' and again, 'A glorious high throne from the beginning, is the place of our sanctuary; O Lord, the Hope of Israel, all that forsake You shall be ashamed, and they that depart from Me shall be written in the earth, because they have forsaken the Lord, the Fountain of living waters;' and in the book of Baruch it is written, 'You have forsaken the Fountain of wisdom,'— this implies that life and wisdom are not foreign to the Essence of the Fountain, but are proper to It, nor were at any time without existence, but were always. Now the Son is all this, who says, 'I am the Life,' and, 'I Wisdom dwell with prudence.' Is it not then irreligious to say, 'Once the Son was not?' for it is all one with saying, 'Once the Fountain was dry, destitute of Life and Wisdom.' But a fountain it would then cease to be; for what begets not from itself, is not a fountain. What a load of extravagance! For God promises that those who do His will shall be as a fountain which the water fails not, saying by Isaiah the prophet, 'And the Lord shall satisfy your soul in drought, and make your bones fat; and you shall be like a watered garden, and like a spring of water, whose waters fail not.' And yet these, whereas God is called and is a Fountain of wisdom, dare to insult Him as barren and void of His proper Wisdom. But their doctrine is false; truth witnessing that God is the eternal Fountain of His proper Wisdom; and, if the Fountain be eternal, the Wisdom also must needs be eternal. For in It were all things made, as David says in the Psalm, 'In Wisdom have You made them all;' and Solomon says, 'The Lord by Wisdom has formed the earth, by understanding has He established the heavens.' And this Wisdom is the Word, and by Him, as John says, 'all things were made,' and 'without Him was made not one thing. ' And this Word is Christ; for 'there is One God, the Father, from whom are all things, and we for Him; and One Lord Jesus Christ, through whom are all things, and we through Him.' And if all things are through Him, He Himself is not to be reckoned with that 'all.' For he who dares to call Him, through whom are things, one of that 'all,' surely will have like speculations concerning God, from whom are all. But if he shrinks from this as unseemly, and excludes God from that all, it is but consistent that he should also exclude from that all the Only-Begotten Son, as being proper to the Father's essence. And, if He be not one of the all, it is sin to say concerning Him, 'He was not,' and 'He was not before His generation.' Such words may be used of the creatures; but as to the Son, He is such as the Father is, of whose essence He is proper Offspring, Word, and Wisdom. For this is proper to the Son, as regards the Father, and this shows that the Father is proper to the Son; that we may neither say that God was ever without Word, nor that the Son was non-existent. For wherefore a Son, if not from Him? Or wherefore Word and Wisdom, if not ever proper to Him?
Source: Four Discourses Against the Arians (New Advent)