In popular works, Nestorianism is often defined as the idea that Christ is two persons. While it is probably inaccurate to attribute this specific idea to Nestorius himself, it is important to note that what he did teach is equally unorthodox. Nestorius’ emphasis on the distinction between the two natures of Christ led him to describe the incarnation in ways that were clearly unsound and profoundly unbiblical. In his first sermon against the theotokos title, for example, he said, “If you want to lift up someone who is lying down, do you not touch body with body and, by joining yourself to the other person, lift up the hurt one while you, joined to him in this fashion, remain what you were? This is the way to think of the mystery of the incarnation.” Nestorius here compares the union of the two natures of Christ to a hug. Nestorius’ loose view of the union of Christ’s natures made Cyril’s response necessary in order to preserve orthodox Christianity.
In direct contrast to Nestorius, Theodore, and Diodore, Cyril insisted on a single-subject Christology. According to Cyril, both Scripture and the Nicene Creed make it clear that the divine Son, the second person of the Trinity, is the one subject who became incarnate. He argued that it was this One, the second person of the Trinity, who was “made flesh and dwelt among us” (John 1:14 KJV). He argued that according to the Nicene Creed, we believe in “one Lord Jesus Christ, the only-begotten Son of God,” and that it is this one, only-begotten Son of God “who, for us men and for our salvation, came down from heaven, and was incarnate by the Holy Spirit of the virgin Mary, and was made man, and was crucified also for us under Pontius Pilate.”
When we read the Gospels, according to Cyril, we do not see the Son of Mary saying and doing some things while the Son of God says and does others. The One we encounter in the Gospels is this one, eternal, divine Son who assumed a true human nature and dwelt among us. Therefore, according to Cyril, it is proper to use the title theotokos, not because the divine nature came into being through Mary, but because the one born to Mary is God incarnate. The title theotokos says something about the identity of Jesus. Whereas Nestorius proclaimed, “I refuse to acknowledge as God, an infant of two or three months old,” Cyril’s theology was consistent with the worship of the infant Christ described in Scripture (Matt. 2:1–2).
Cyril explained the union of the two natures in Christ using the idea of a hypostatic union in which the second hypostasis of the Trinity (the one eternal Son), who has a perfect divine nature from all eternity, assumed a true and complete human nature in the womb of Mary. After the incarnation, the one hypostasis (the one person, the single subject), now has two natures (divine and human). This explains why the Gospels can attribute to the one person of Christ acts and words proper to the human nature as well as acts and words proper to the divine nature. Anything that can be ascribed to either nature can be ascribed to the one person because both natures truly belong to the one person. The attributes of either nature, however, cannot be ascribed to the other nature. Cyril argued that we do not say that the divine nature can be born, hunger, thirst, suffer, or die. Nor do we say that Christ’s human nature has existed eternally. But we can, by virtue of the communication of attributes (communicatio idiomatum), ascribe all of these things to the one person.
The hypostatic union helps us understand why Scripture will sometimes ascribe something proper to one nature to the one person while using the name of the person that is proper to the other nature. As the Westminster Confession of Faith explains, “By reason of the unity of the person, that which is proper to one nature, is sometimes in Scripture attributed to the person denominated by the other nature” (8.7). Acts 20:28, for example, can speak of the “blood of God,” and Paul, in 1 Corinthians 2:8 can speak of those who “crucified the Lord of glory.” The names God and Lord are usually used in Scripture in association with the divine nature, and yet in Acts 20:28 and 1 Corinthians 2:8, Scripture ascribes attributes and activities of the human nature to those names. The divine nature does not have blood and it does not have the capacity to be crucified, but the human nature does. But since the names God and Lord, though most often used in conjunction with the divine nature, are names for the one person of Christ, Scripture can ascribe attributes and activities of the human nature to God and to Lord. That is not because these attributes and activities belong to the divine nature but because they belong to the human nature of Christ, which since the incarnation belongs to the Son of God as much as the divine nature has always belonged to the Son.
So we cannot simply dismiss Cyril as one of many notable church fathers. You may never have heard of Cyril, but every time you confess our Savior, Jesus, as one person in two distinct natures, you have reason to thank God for Cyril’s theological legacy.