But perhaps you will say that this grace of our Lord Jesus Christ, of which the Apostle writes, was not born with Him, but was afterwards infused into Him by the descent of Divinity upon Him, since you say that the man Jesus Christ our Lord (whom you call a mere man) was not born with God, but afterwards was assumed by God: 2414 and that through this grace was given to the man at the same time that Divinity was given to Him. Nor do we say anything else than that Divine grace descended with the Divinity, for the Divine grace of God is in a way a bestowal of actual Divinity and a gift of a liberal supply of graces. Perhaps then it may be thought that the difference between us is one of time rather than of what is essential, since the Divinity which we say was born with Jesus Christ you say was afterwards infused into Him. But the fact is that if you deny that Divinity was born with the Lord you cannot afterwards make a confession according to the faith; for it is an impossibility for one and the same thing to be partly impious and also to turn out partly pious, and for the same thing partly to belong to faith and partly to misbelief. To begin with then I ask you this: Do you say that our Lord Jesus Christ, who was born of the Virgin Mary is only the Son of man, or that He is the Son of God as well? For we, I mean all who hold the Catholic faith, all of us, I say, believe and are sure and know and confess that He is both, i.e., that He is Son of man because born of a woman and Son of God because conceived of Divinity. Do you then admit that He is both, i.e., Son of God and Son of man, or do you say that He is Son of man only? If Son of man only then there cry out against you apostles and prophets, aye and the Holy Ghost Himself, by whom the conception was brought about. That most shameless mouth of yours is stopped by all the witnesses of the Divine decrees: it is stopped by sacred writings and holy witnesses: aye and it is stopped by the very gospel of God as if by a Divine hand. And that mighty Gabriel who in the case of Zacharias restrained the voice of unbelief by the power of his word, much more strongly condemned in your case the voice of p. 562 blasphemy and sin, by his own lips, saying to the Virgin Mary, the mother of God: “The Holy Ghost shall come upon thee, and the power of the Most High shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God.” 2415 Do you see how Jesus Christ is first proclaimed to be the Son of God that according to the flesh He might become the Son of man? For when the Virgin Mary was to bring forth the Lord she conceived owing to the descent of the Holy Spirit upon her and the cooperation of the power of the Most High. And from this you can see that the origin of our Lord and Saviour must come from thence, whence His conception came; and since He was born owing to the descent of the fulness of Divinity in Its completeness upon the Virgin, He could not be the Son of man unless He had first been the Son of God; and so the angel when sent to announce His nativity and sacred birth, when he had already spoken of the mystery of His conception added a word expressive of His birth, saying: “Therefore also that holy thing which shall be born of thee shall be called the Son of God” [i.e., He shall be called the Son of Him from whom He was begotten]. 2416 Jesus Christ is therefore the Son of God, because He was begotten of God and conceived of God. But if He is the Son of God, then most certainly He is God: but if He is God, then He is not lacking in the grace of God. Nor indeed was He ever lacking in that of which He is Himself the maker. For grace and truth were made by Jesus Christ.
Nestorius maintained that “that which was formed in the womb of Mary was not God Himself…but because God dwells in him whom He has assumed, therefore also He who is assumed is called God because of Him who assumes Him. And it is not God who has suffered, but God was united with the crucified flesh.” (Fragm. in Marius Mercator p. 789 sq. (ed. Migne).) Thus he made out that in Christ were two Persons, one assuming and the other assumed.562:2415
S. Luke i. 35.562:2416