De Synodis 76

VI. "And if any one grant the Son only a likeness of activity, but rob Him of the likeness of essence which is the corner-stone of our faith, in spite of the fact that the Son Himself reveals His essential likeness with the Father in the words, For as the Father hath life in Himself, so also hath He given to the Son to have life in Himself, as well as His likeness in activity by teaching us that What things soever the Father doeth, these also doeth the Son likewise, such a man robs himself of the knowledge of eternal life which is in the Father and the Son, and let him be anathema." 19. The heretics when beset by authoritative passages in Scripture are wont only to grant that the Son is like the Father in might while they deprive Him of similarity of nature. This is foolish and impious, for they do not understand that similar might can only be the result of a similar nature. For a lower nature can never attain to the might of a higher and more powerful nature. What will the men who make these assertions say about the omnipotence of God the Father, if the might of a lower nature is made equal to His own? For they cannot deny that the Son's power is the same, seeing that He has said What things soever the Father doeth, these also doeth the Son likewise. No, a similarity of nature follows on a similarity of might when He says, As the Father hath life in Himself, so also hath He given to the Son to have life in Himself. In life is implied nature and essence; this, Christ teaches, has been given Him to have as the Father hath. Therefore similarity of life contains similarity of might: for there cannot be similarity of life where the nature is dissimilar. So it is necessary that similarity of essence follows on similarity of might: for as what the Father does, the Son does also, so the life that the Father has He has given to the Son to have likewise. Therefore we condemn the rash and impious statements of those who confess a similarity of might but have dared to preach a dissimilarity of nature, since it is the chief ground of our hope to confess that in the Father and the Son there is an identical divine substance.