The hypostatic union enables us to ascribe to God what belongs to the flesh in Christ.
How then is Christ (whom you term a mere man) proclaimed in Holy Scripture to be God without beginning, if by our own confession the Lords manhood 2581 did not exist before His birth and conception of a Virgin? And how can we read of so close a union of man and God, as to make it appear that man was ever co-eternal with God, and that afterwards God suffered with man: whereas we cannot believe that man can be without beginning or that God can suffer? It is this which we established in our previous writings; viz., that God being joined to manhood, 2582 i.e., to His own body, does not allow any separation to be made in mens thoughts between man and God. Nor will He permit anyone to hold that there is one Person of the Son of man, and another Person of the Son of God. But in all the holy Scriptures He joins together and as it were incorporates in the Godhead, the Lords manhood, 2583 so that no one can sever man from God in time, nor God from man at His Passion. For if you regard Him in time, you will find that the Son of man is ever with the Son of God. If you take note of His Passion, you will find that the Son of God is ever with the Son of man, and that Christ the Son of man and the Son of God is so one and indivisible, that, in the language of holy Scripture, the man cannot be severed in time from God, nor God from man at His Passion. Hence comes this: “No man hath ascended into heaven, but He who came down from heaven, even the Son of man who is in heaven.” 2584 Where the Son of God while He was speaking on earth testified that the Son of man was in heaven: and testified that the same Son of man, who, He said, would ascend into heaven, had previously come down from heaven. And this: “What and if ye shall see the Son of man ascend up where He was before,” 2585 where He gives the name of Him who was born of man, but affirms that He ever was up on high. And the Apostle also, when considering what happened in time, says that all things were made by Christ. For he says, “There is one Lord Jesus Christ, by whom are all things.” 2586 But when speaking of His Passion, he shows that the Lord of glory was crucified. “For if,” he says, “they had known, they would never have crucified the Lord of glory.” 2587 And so too the Creed speaking of the only and first-begotten Lord Jesus Christ, “Very God of Very God, Being of one substance with the Father, and the Maker of all things,” affirms that He was born of the Virgin and crucified and afterwards buried. Thus joining in one body (as it were) the Son of God and of man, and uniting God and man, so that there can be no severance either in time or at the Passion, since the Lord Jesus Christ is shown to be one and the same Person, both as God through all eternity, and as man through the endurance of His Passion; and though we cannot say that man is without beginning or that God is passible, yet in the one Person of the Lord Jesus Christ we can speak of man as eternal, and of God as dead. You see then that Christ means the whole Person, and that the name represents both natures, for both man and God are born, and so it takes in the whole Person so that when this name is used we see that no part is left out. There was not then before the birth of a Virgin the same eternity belonging in the past to the manhood as to the Divinity, but because Divinity was united to manhood in the womb of the Virgin, it follows that when we use the name of Christ one cannot be spoken of without the other.
Dominicus homo, see above on V. v.602:2582
S. John iii. 13.602:2585
S. John vi. 63.602:2586
1 Cor. viii. 6.602:2587
1 Cor. ii. 8. See the note on IV. vii.