Nestorius accused Cyril of Alexandria of turning the nature of the Godhead into flesh: “To speak briefly, they refer the Godhead of the Only-begotten to the same origin as the flesh joined [with it], and kill it with the flesh, and blasphemously say that the flesh joined with the Godhead was turned into deity by the deifying Word, which is nothing more nor less than to corrupt both.”:”(“The First Letter of Nestorius to Celestine,” in Christology of the Later Fathers, ed. Edward Rochie Hardy [Philadelphia: The Westminster Press, 1954], pp. 347-348.)”:
Building on the Nicene Creed, Cyril of Alexandria ably answers this calumny:
…taking the flesh of the holy Virgin, and making it his own from the womb, he underwent a birth like ours, and came forth a man of woman, not throwing off what he was, but even though he became [man] by the assumption of flesh and blood, yet still remaining what he was, that is, God indeed in nature and truth. We do not say that the flesh was changed into the nature of Godhead, nor that the ineffable nature of the Word of God was transformed into the nature of flesh, for he is unchangeable and unalterable, always remaining the same according to the Scriptures. But when seen as a babe and wrapped in swaddling clothes, even when still in the bosom of the Virgin who bore him, he filled all creation as God, and was enthroned with him who begot him. For the Divine cannot be numbered or measured, and does not admit of circumscription.:”(“The Third Letter of Cyril to Nestorius,” in ibid., pg. 350)”:
It’s interesting to me that Nestorius wanted passionately to avoid “fusing” the deity and humanity in a way that would seem to court the Arian or Apollinarian heresies, but to avoid those errors he wound up separating the deity and humanity, essentially making Christ into two persons. Cyril, on the other hand, wanted passionately to avoid a union of mere “dignity and authority” such that the unity of the Mediator would be destroyed and human redemption imperiled. Nevertheless, the Alexandrian school, of which Cyril was the best advocate, had its problems, too. According to one scholar the Alexandrians “do not emphasize the fullness and the active autonomy of the humanity of Christ,” and in Cyril’s description of the natures of Christ, “one physis of the Word of God,” there is ambiguous enough to allow for Monophysitism to later develop from it.:”(Roch A. Kereszty, O.Cist., Jesus Christ: Fundamentals of Christology, rev. and updated [St. Paul's, 2002], pg. 236.)”: On the other hand, the Antiochene school, of which Nestorius was a member, had an “inability to express with sufficient clarity the ontological unity of Christ and to show that this unity is based on the one ontological subject of God the Word.”:”(Ibid., 238.)”:
Again, too much emphasis on one part of the Truth, such that one starts to see the whole of the Truth as being a function of the one aspect one feels most important, seems inevitably to lead to distortion, and sometimes, to outright heresy.