Book Four — Salvation, Chapter 34 — Summa Contra Gentiles
[1] From the things set down, therefore, it appears that Christ was not without divine nature, as Ebion, Cerinthus, and Photinus said; nor without a true human body, as in the error of Mani and Valentine; nor without a human soul, as Arius and Apollinaris held. Since, then, these three substances met in Christ—namely, divinity, the human soul, and the true human body—what one should think about their union following the Scriptural teachings remains for inquiry.
[2] Now, then, Theodore of Mopsueste and Nestorius, his follower, offered one sort of opinion on the aforesaid union. They said that the human soul and the true human body came together in Christ by a natural union to constitute one man of the same species and nature with other men, and that in this man God dwelt as in His temple, namely, by grace, just as in other holy men. Hence, it says in John (2:19, 21), that He said to the Jews: “Destroy this temple and in three days I will raise it up”; and later the Evangelist by way of exposition adds: “But he spoke of the temple of His body”; and the Apostle says: “In Him it has well pleased the Father, that all fullness should dwell” (Col. 1:19). And out of these arose further a certain affective union between that man and God, when that man cleaved to God with his own good will, and God lifted up that man with His will, in the words of John (8:29): “He that sent me is with me, and He has not left me alone: for I do always the things that please Him.” Let one thus understand that the union of that man to God is such as was the union of which the Apostle said: “He who is joined to God is one spirit” (1 Cor. 6:17). And just as, from the latter union, names which properly befit God are transferred to men so that they are called “gods,” and “sons of God,” and “lords,” and “holy ones,” and “christs”—as is clear from a diversity of places in Scripture; so also the divine names befit that man so that, by reason of God’s indwelling and the affective union, he is called God, and the Son of God, and Holy, and Christ. Nonetheless, because there was in that man a greater fullness of grace than in other holy men, he was before all the rest the temple of God, he was united to God, more closely in affection, and it was by a singular kind of privilege that he shared the divine names. And because of this outstanding grace he was established in a share of the divine dignity and honor—namely, that he be co-adored with God. So, then, consequently on the things just said there must be one Person of the Word of God, and another person of that man who is co-adored with the Word of God. And if one Person of each of the two be mentioned, this will be by reason of the affective union aforesaid; so that man and the Word of God may be called one Person, as is said of man and woman that “now they are not two, but one flesh” (Mat. 19:6).
Now, such a union does not bring it about that what is said of the first can be said of the second (for not everything which becomes the man is true of the woman, or conversely); therefore in the union of the Word and that man they think this must be observed: The things proper to that man and pertinent to the human nature cannot be said becomingly of God’s Word, or of God. just so it becomes that man that he was born of a virgin, that he suffered, died, was buried, and this kind of thing; and all of these, they assert, ought not be said of God, or of the Word of God. But, since there are certain names which, although they are chiefly befitting to God, are nonetheless communicated to men in a fashion—“christ,” for instance, “lord,” “holy,” and even “son of God”—nothing according to them keeps one from the use of such names in predication of the things just mentioned. For, according to them, we say fittingly that Christ, or the “Lord of glory,” or the “Saint of saints,” or “God’s son” was born of a virgin, suffered, died and was buried. Hence, too, the Blessed Virgin must not be named the mother of God, or of the Word of God, but the mother of Christ, they say.
[3] But let one earnestly consider the matter and he will see that the position described excludes the truth of the Incarnation. For, in that position, the Word of God was united to that man only through an indwelling by grace, on which a union of wills follows. But the indwelling of God’s Word in a man is not for God’s Word to be made flesh. For the Word of God and God Himself have been dwelling in all the holy men since the world was founded; as the Apostle says: “You are the temple of the living God; as God says: I will dwell in them” (2 Cor. 6: 16). And this indwelling, for all that, cannot be called incarnation; otherwise, God would have repeatedly been made flesh since the beginning of the world. Nor does it suffice for the notion of incarnation if the Word of God or God dwelt in that man with a fuller grace, for “greater and less do not diversify the species of union.” Since the Christian religion is based on faith in the Incarnation, it is now quite evident that the position described removes the basis of the Christian religion.