5. Whence then is the Father greater? For if greater, He is greater by greatness; but whereas the Son is His greatness, neither assuredly is the Son greater than He who begat Him, nor is the Father greater than that greatness, whereby He is great; therefore they are equal. For whence is He equal, if not in that which He is, to whom it is not one thing to be, and another to be great? Or if the Father is greater in eternity, the Son is not equal in anything whatsoever. For whence equal? If you say in greatness, that greatness is not equal which is less eternal, and so of all things else. Or is He perhaps equal in power, but not equal in wisdom? But how is that power which is less wise, equal? Or is He equal in wisdom, but not equal in power? But how is that wisdom equal which is less powerful? It remains, therefore, that if He is not equal in anything, He is not equal in all. But Scripture proclaims, that “He thought it not robbery to be equal with God.” Therefore any adversary of the truth whatever, provided he feels bound by apostolical authority, must needs confess that the Son is equal with God in each one thing whatsoever. Let him choose that which he will; from it he will be shown, that He is equal in all things which are said of His substance.
Complete source paragraph · On the Holy Trinity, Chapter 3.—That the Unity of the Essence of the Father and the Son is to Be Gathered from the Words, “We are One.” The Son is Equal to the Father Both in Wisdom and in All Other Things.; original source section: Chapter 3, source paragraph 3 · Original source