Gregory further shows that the Only-Begotten being begotten not only of the Father, but also impassibly of the Virgin by the Holy Ghost, does not divide the substance; seeing that neither is the nature of men divided or severed from the parents by being begotten, as is ingeniously demonstrated from the instances of Adam and Abraham
But he says, “Not dividing His own essence by begetting, and being at once begetter and begotten, at the same time Father and Son; for He is incorruptible.” Most cogent conclusion! What do you mean, most sapient sir? Because He is incorruptible, therefore He does not divide His own essence by begetting the Son: nor does He beget Himself or be begotten of Himself, nor become at the same time His own Father and His own Son because He is incorruptible. It follows then, that if any one is of corruptible nature he divides his essence by begetting, and is begotten by himself, and begets himself, and is his own father and his own son, because he is not incorruptible. If this is so, then Abraham, because he was corruptible, did not beget Ishmael and Isaac, but begot himself by the bondwoman and by his lawful wife or, to take the other mountebank tricks of the argument, he divided his essence among the sons who were begotten of him, and first, when Hagar bore him a son, he was divided into two sections, and in one of the halves became Ishmael, while in the other he remained half Abraham; and subsequently the residue of the essence of Abraham being again divided took subsistence in Isaac. Accordingly the fourth part of the essence of Abraham was divided into the twin sons of Isaac, so that there was an eighth in each of his grandchildren! How could one subdivide the eighth part, cutting it small in fractions among the twelve Patriarchs, or among the threescore and fifteen souls with whom Jacob went down into Egypt? And why do I talk thus when I really ought to confute the folly of such notions by beginning with the first man? For if it is a property of the incorruptible only not to divide its essence in begetting, and if Adam was corruptible, to whom the word was spoken, “Dust you are and unto dust shall you return,” then, according to Eunomius' reasoning, he certainly divided his essence, being cut up among those who were begotten of him, and by reason of the vast number of his posterity (the slice of his essence which is to be found in each being necessarily subdivided according to the number of his progeny), the essence of Adam is used up before Abraham began to subsist, being dispersed in these minute and infinitesimal particles among the countless myriads of his descendants, and the minute fragment of Adam that has reached Abraham and his descendants by a process of division, is no longer discoverable in them as a remnant of his essence, inasmuch as his nature has been already used up among the countless myriads of those who were before them by its division into infinitesimal fractions. Mark the folly of him who “understands neither what he says nor whereof he affirms.” For by saying “Since He is incorruptible” He neither divides His essence nor begets Himself nor becomes His own father, he implicitly lays it down that we must suppose all those things from which he affirms that the incorruptible alone are free to be incidental to generation in the case of every one who is subject to corruption. Though there are many other considerations capable of proving the inanity of his argument, I think that what has been said above is sufficient to demonstrate its absurdity. But this has surely been already acknowledged by all who have an eye for logical consistency, that, when he asserted incorruptibility of the Father alone, he places all things which are considered after the Father in the category of corruptible, by virtue of opposition to the incorruptible, so as to make out even the Son not to be free from corruption. If then he places the Son in opposition to the incorruptible, he not only defines Him to be corruptible, but also asserts of Him all those incidents from which he affirms only the incorruptible to be exempt. For it necessarily follows that, if the Father alone neither begets Himself nor is begotten of Himself, everything which is not incorruptible both begets itself and is begotten of itself, and becomes its own father and son, shifting from its own proper essence to each of these relations. For if to be incorruptible belongs to the Father alone, and if not to be the things specified is a special property of the incorruptible, then, of course, according to this heretical argument, the Son is not incorruptible, and all these circumstances of course, find place about Him—to have His essence divided, to beget Himself and to be begotten by Himself, to become Himself His own father and His own son.
Perhaps, however, it is waste of time to linger long over such follies. Let us pass to the next point of his statement. He adds to what he had already said, “Not standing in need, in the act of creation, of matter or parts or natural instruments: for He stands in need of nothing.” This proposition, though Eunomius states it with a certain looseness of phrase, we yet do not reject as inconsistent with godly doctrine. For learning as we do that “He spoke the word and they were made: He commanded and they were created,” we know that the Word is the Creator of matter, by that very act also producing with the matter the qualities of matter, so that for Him the impulse of His almighty will was everything and instead of everything, matter, instrument, place, time, essence, quality, everything that is conceived in creation. For at one and the same time did He will that that which ought to be should be, and His power, that produced all things that are, kept pace with His will, turning His will into act. For thus the mighty Moses in the record of creation instructs us about the Divine power, ascribing the production of each of the objects that were manifested in the creation to the words that bade them be. For “God said,” he tells us, “Let there be light, and there was light:” and so about the rest, without any mention either of matter or of any instrumental agency. Accordingly the language of Eunomius on this point is not to be rejected. For God, when creating all things that have their origin by creation, neither stood in need of any matter on which to operate, nor of instruments to aid Him in His construction: for the power and wisdom of God has no need of any external assistance. But Christ is “the Power of God and the Wisdom of God,” by Whom all things were made and without Whom is no existent thing, as John testifies. If, then, all things were made by Him, both visible and invisible, and if His will alone suffices to effect the subsistence of existing things (for His will is power), Eunomius utters our doctrine though with a loose mode of expression. For what instrument and what matter could He Who upholds all things by the word of His power need in upholding the constitution of existing things by His almighty word? But if he maintains that what we have believed to be true of the Only-begotten in the case of the creation, is true also in the case of the Son— in the sense that the Father created Him in like manner as the creation was made by the Son—then we retract our former statement, because such a supposition is a denial of the Godhead of the Only-begotten. For we have learned from the mighty utterance of Paul that it is the distinguishing feature of idolatry to worship and serve the creature more than the Creator, as well as from David, when He says “There shall no new God be in you: neither shall you worship any alien God.” We use this line and rule to arrive at the discernment of the object of worship, so as to be convinced that that alone is God which is neither “new” nor “alien.” Since then we have been taught to believe that the Only-begotten God is God, we acknowledge, by our belief that He is God, that He is neither “new” or “alien.” If, then, He is God, He is not “new,” and if He is not new, He is assuredly eternal. Accordingly, neither is the Eternal “new,” nor is He Who is of the Father and in the bosom of the Father and Who has the Father in Himself “alien” from true Deity. Thus he who severs the Son from the nature of the Father either absolutely disallows the worship of the Son, that he may not worship an alien God, or bows down before an idol, making a creature and not God the object of his worship, and giving to his idol the name of Christ.
Source: Against Eunomius (New Advent)