Cyril of Alexandria, Nestorius’ great opponent, focused on this failure as worthy of the strongest anathematization. As he saw it, he himself was simply continuing the work of the Council of Nicea, which had already decided that Christ, the only-begotten Son, was true God of true God and, as John’s Gospel teaches, was the Word made flesh. Cyril rejected Nestorius’ view that the union of the natures was the result of a combination of the grace of God and the obedience of man. This seemed to Cyril to make of the one Christ two persons: “a man in his own person dignified with the name Son and the Word which is of God in His own person posessing by nature the name Son” (Davis, pg. 150). But, Davis continues his summary, “Scripture does not say that the Word united himself to the person of man but that He became flesh, that is, He became partaker of flesh and blood like us.” Accordingly,
Cyril confessed a personal union of the Word with the flesh not merely with a man who carried God with him. United by a union of natures, the Word brought about an indwelling such as the soul of man has with the body. In the Incarnation a man is not conjoined with God in a unity of dignity and honor; neither conjunction nor juxtaposition is adequate to signify this mode of union. In the Eucharist we receive not ordinary flesh nor the flesh of a man associated with the Word by a unity of dignity or indwelling but the very flesh of the Word Himself. (ibid.).
This personal union of the natures seems to be the reason why the traditional title for Mary, “Theotokos” (God-Bearer) was so strongly insisted upon by the orthodox. Says Davis, summarizing Cyril:
The Word has been personally united to the flesh; the same person is both God and man. The human and divine in the one Christ cannot be divided nor connected merely by common dignity, authority or rule. One cannot attribute the expressions of Scripture now to the man apart from the Word, now exclusively to the Word. Christ is not just man carrying God within him. One cannot say that the Word is God or Master of Christ; rather one must confess Christ to be both God and man alike. Jesus is not just a man actuated by the Word or invested with His glory. Word and man are not worshipped jointly, but are accorded one worship…The Word Himself became our high priest, not the man separate from Him. The flesh of the Lord is life-giving, for it is the flesh of the Word of God. The Word suffered, was crucified, tasted death and rose in the flesh. (ibid, pg. 151)
Consequently, it must be understood that Mary gave birth to the person of the Word of God made flesh, who was, as Nicea had authoritatively pronounced, true God of true God. Ergo, Mary bore God, not merely Nestorius’ prosopon “Christ.” Cyril described the union of the natures in the Word made flesh as the “hypostatic union” because the natures were united in one hypostasis, one person. Davis cites G.L. Prestige on the results of the hypostatic union for Christ’s personality: “The deity has its personality and the manhood its personality, but the two personalities are identically one and the same….The reason why the two are identical is because the human personality is simply that of the divine subject under submission to physical conditions” (pg. 152).
Still, Davis says that a big problem with Cyril’s Christology was that he refused to distinguish between the terms hypostasis and nature. “Nature was for him the equivalent of hypostasis, a concrete, objective existence” (ibid.). He felt that speaking of “two natures” involved separation, and so he “made his own the Apollinarian formula–one incarnate nature of the divine Word–found in pseudopigraphical books, thinking that it came from Athanasius” (pg. 153).