Basil: Contra Eunomius 1.18

Hence through this one blasphemy he rejects all terms handed down by the Holy Spirit for the glorification of the Only-Begotten, even though the gospel teaches that the Father, God, has set his seal upon him (John 6.27), and the Apostle that he is the image of the invisible God (Col. 1.15). He is not a lifeless image, nor handmade, nor a product of art or conceptualisation, but a living image, or rather self-existent life which always preserves the indistinguishability, not by likeness of shape, but in his very substance. In my opinion, I say that existing in the form of God (Phil 2.6) means the same as “existing in the substance of God.” For just as having taken up the form of a slave (Phil. 2.7) signifies that our Lord was begotten in the substance of humanity, so too saying existing in the form of God (Phil. 2.6) certainly reveals the distinctive feature of the divine substance.The one who sees me, he says, sees the Father (John 14.9).

When Eunomius alienates the Only-Begotten from the Father and utterly separates him from fellowship with the Father, he cuts off (insofar as he can) the way upward to knowledge that occurs through the Son. While the Lord says: All that the Father has is mine (John 17.9), Eunomius says that the Father has no fellowship whatsoever with the one who comes from him. In addition, the Lord himself has taught us that as the Father has life in himself, so he has granted also to the Son to have life in himself (John 5.26). But what has Eunomius taught us? That the one who is begotten has no comparison with the one who has begotten him. Through this one statement he once and for all does away with the account of the image and denies that the Son is the Father’s radiance and the character of his subsistence (Hebrews 1.3). Now it is impossible to conceive and image of something that in incomparable or for there to be a radiance of something with which it has not fellowship by nature. But once again, he persists in the same kind of scheme, saying that “the unbegotten has no comparison with the begotten.” He does not say “the Father has no comparison with the one from him” in order to demonstrate the opposition between these words, thereby transferring this opposition to the very substance of the Father and the Son.