The Council of Ephesus in 431 declared that Jesus is one person, acting and named as one person. There was a debate between Nestorius and Cyril. Nestorius believed that Mary should be called the mother of Christ, not the mother of God, and that different names should be used for different expressions of Jesus. Cyril argued that Mary is indeed the mother of God, emphasizing the unity of Jesus as one person. Cyril also explained the concept of paradoxical predicates, where different actions can be attributed to Jesus based on his two natures. The Council of Ephesus supported Cyril, affirming the unity of the divine son of God.
The Council of Ephesus in 431 established that Jesus is one person, so he acts as one person and he is named as one person. The unity of the person of Christ was used throughout play, and you can see it in the answer to one simple question, so here's a question. Is Mary the mother of God? The word was theotakos, and actually should be rendered the bearer of God, so is Mary the bearer of God? When a new bishop took office in Constantinople, he was asked this question, and he replied, no, we ought not say Mary is the mother of God, but rather the mother of Christ, and he maintained that we should use names of Jesus which are appropriate to whatever expression we are giving of him.
His name was Nestorius, and he had a whole taxonomy for this, and he thought scripture itself set forth the example for us. One example he liked was when Jesus said, destroy this temple, and in three days I will raise it again. Nestorius said, he didn't say, destroy this godhead, he said, destroy this temple. Therefore we ought to follow suit and only use names for Jesus which are natural to his humanity, like Messiah, Christ, Lord, and Jesus, when we are referring to human actions.
That was Nestorius. The bishop of Alexandria at the time was a man by the name of Cyril, and he objected vociferously. He said, we absolutely can and should say that Mary is the mother of God, and he raised this objection based on the unity of the Son. He said that there were two critical mistakes that Nestorius made. First of all, natures don't do actions, only persons do actions. So it's not like Jesus' humanity does one thing and his deity does another, instead any time we ask the question, who did it, when we read the life of Christ in the Gospels, the answer is always one and the same person, Jesus.
So that's the first thing, Jesus acts as one person. The second thing is, Jesus is named as one person. Any time you find the name of Jesus in a sentence, you can always change it out, you can always change out his name with any other designation for Jesus and the sentence will still be Christologically correct. And this is because of the unity of his person. So who died? Jesus did, right? Is God an accurate designation for Jesus? Yes, so then it's accurate to say that God died.
Or let's try another one, who upholds the universe by the word of his power? Jesus does. Well, Jesus can also accurately be described as a man from Nazareth, right? So then it's accurate to say a man from Nazareth upholds the universe by the word of his power. These are called paradoxical predicates, and they are sometimes found in scripture, like when Acts 20, 28 speaks of the blood of God. Now, why are they paradoxical? Because it's still okay to predicate different actions of Jesus according to his two natures.
It's true that Jesus died predicated on his humanity, in the same way Jesus upholds the universe according to his deity. So he is immutable with respect to his deity. He experiences change with respect to his humanity. So this work of distinguishing his actions is sometimes called partitive exegesis, and it was a long-standing tradition in the Antiochian tradition, going back to Gregory of Nazianzus. Nestorius was well-educated in this tradition, and there's a chance he just misinterpreted his own tradition.
So whereas they predicated birds, he distinguished between persons. The council of Ephesus stood on the side of Cyril of Alexandria over against Nestorius, defending the unity of the one divine son of God.
