Nestorianism is the belief that the two natures of Christ are not inseparately united to his person or hypostasis. This belief is a result of denying the communicatio idiomatum which states that the properties or attributes of both natures are communicated to the one person who is Christ. But in the communicatio idiomatum, the two natures are not communicated to each other which would blur the distinction between the humanity and deity of Christ. Nestorianism speaks of Christ as if he were two persons: the divine Logos and the man Jesus Christ. The end result of this belief is that the man who is Christ is not the same person as the eternal Logos who is God.
The first proponent of Nestorianism appears to be Theodore of Mopsuestia. He taught that it was only the man Jesus Christ who suffered on the cross, not the eternal Logos who is God since God is impassible or incapable of suffering. According to him, we should never speak of God dying on the cross for us because God is immortal. Cyril of Alexandria reproduces some of his statements regarding his beliefs about the relationship between the Word of God and the man who is Christ:
“And it is convenient that they who view aright, should, when we are looking for natural forefathers, call neither God the Word son of David or Abraham but their Maker: nor the body before the ages out of the Father but the seed of Abraham and David born from Mary. And then the consideration is of natural births, neither is God the Word deemed to be Mary’s son: for mortal bears what is mortal by nature and a body like itself. . . . Nor does God the Word Himself please that He should be David’s son, but lord; but that the body should be called son of David” (Second Book Against Theodore 13).
So God the Word is not the son of David or Mary’s son, but only the body of Christ. This means Mary only gave birth to the man Jesus but not the eternal God of the universe who has no beginning. The argument is that if Mary gave birth to the eternal Son of God, he would no longer be eternal since he would have a beginning. Since God has always existed, Mary could not have given birth to God. He also says concerning the Son:
“None, he says, hath He made partaker of the Son’s dignity. For in this that He said, I begat Thee, He gave as it were through it a participation of sonship, yet this which has been said is openly shewn to have nothing at all to do with God the Word” (Third Book Against Theodore 5).
Theodore believed that when God the Father bestowed on the Son the name that is above every name at his ascension, it was not upon God the Word that this was done since he already is God, but only the man Jesus Christ.
These beliefs were passed down from him to Nestorius who objected to the phrase theotokos or “mother of God” for Mary since God has no beginning. He instead proposed the title Christotokos “mother of Christ.” But what we need to understand about this controversy is that the title “mother of God” was originally a Christological statement, not a Mariological one. The purpose of the phrase at the Council of Ephesus in 431 was to defend the person of Christ against Nestorians who divided the Son into two persons: one human and one divine. Nestorians argued that Mary carried within her the human Jesus, but not the eternal Son of God. The title theotokos “mother of God” was not created to exalt Mary, but to defend the truth that Jesus is fully God and fully man in one person. Over time, the emphasis of the statement shifted from Jesus to Mary. Roman Catholicism has turned it into a basis upon which to venerate Mary in accordance with their belief in hyperdulia. A more accurate title for Mary that captures all of who Jesus is in the incarnation is theanthrōpotokos “mother of the God-man.”
A verse that is relevant for this debate is Luke 1:43 where Elizabeth says: “And why is this granted to me that the mother of my Lord should come to me?” Jesus is identified as “my Lord” even before he is born. Mary is rightly said to be the mother of God in the sense that she is the mother of the God-man Jesus Christ. The one who dwelled in the womb of Mary is the same person who created all things. It is also proper to speak of God dying on the cross for our sins in accordance with Acts 20:28: “to care for the church of God, which he obtained with his own blood.” Yet the suffering of Christ who is God is only with respect to his human nature since God by definition is immortal and cannot die. The solution is not to divide the Son into two persons and say that only the man Jesus Christ died on the cross, but to speak of Christ’s actions being with respect to one of his two natures that are each properly predicated to his person. Thus we can speak of God dying on the cross in the person of Jesus Christ with respect to his human nature. Only a sacrifice of infinite worth could pay the penalty for our sins which deserve infinite punishment.
Modern day proponents of Nestorianism include modalists who divide Jesus into two persons to explain how Jesus can be praying to the Father in John 17. In their view, it is not Jesus praying to the Father who is a distinct person from him, but the human nature of Jesus communicating with his divine nature. Some Protestants also fall into Nestorianism as a result of overreacting to the Roman Catholic exaltation of Mary based on a misuse of the title “mother of God.”