Heresy of the Week

Nestorianism (5th Century)

This heresy about the person of Christ was initiated by Nestorius, bishop of Constantinople, who denied Mary the title of Theotokos (Greek: "God-bearer" or, less literally, "Mother of God"). Nestorius claimed that she only bore Christ’s human nature in her womb, and proposed the alternative title Christotokos ("Christ-bearer" or "Mother of Christ").

Orthodox Catholic theologians recognized that Nestorius’s theory would fracture Christ into two separate persons (one human and one divine, joined in a sort of loose unity), only one of whom was in her womb. The Church reacted in 431 with the Council of Ephesus, defining that Mary can be properly referred to as the Mother of God, not in the sense that she is older than God or the source of God, but in the sense that the person she carried in her womb was, in fact, God incarnate ("in the flesh").

There is some doubt whether Nestorius himself held the heresy his statements imply, and in this century, the Assyrian Church of the East, historically regarded as a Nestorian church, has signed a fully orthodox joint declaration on Christology with the Catholic Church and rejects Nestorianism. It is now in the process of coming into full ecclesial communion with the Catholic Church.

From Catholic Answers.