By Water & Blood

Chapter 6: How the Church of God believes

But those who make it their prayer to believe in the one who has come will recognize these three: the one who is “of the seed of David” and of the holy Virgin; the Son of God who dwelt in him, who pre-existed and subsists essentially (οὐσιωδῶς ὑφεστῶτα); and God, his Father, by whom he himself continually confesses that he was sent. “To us,” then, according to the Apostle, “there is one God, the Father, of whom are all things, and one Lord Jesus Christ, by whom are all things”—the pre-existent only-begotten Son of God; and third, the Son of Man according to the flesh, whom the Son of God assumed for our sake.

But neither was the body which he assumed the same as the Son of God who assumed it, nor could the Son of God himself be thought one and the same with the one who begot him. These three, then, being posited, those who grant two but put the third out of the way would deserve to be cast out of the Church.