The early church heresy of Nestorianism was based on the idea that Jesus Christ has two distinct but united natures, human and divine. Nestorius of Antioch was consecrated as Bishop of Constantinople in A.D. 428. This caused considerable debate among Constantinople's clergy because he was from Syria and chosen over more locally well-known priests. Nestorius' teachings were ultimately denounced by the church at the Council of Ephesus. He was removed from his position and sent back to Antioch, and later to Egypt.
Nestorius Against Arianism
Immediately upon his arrival in Constantinople, Nestorius opposed the heresy of Arianism that he found in the city, a heresy that denied that Jesus is co-equal with God. According to the Catholic Encyclopedia, Nestorius destroyed an Arian chapel just a few days after his consecration. A month later, he convinced Emperor Theodosius to issue an edict against the heresy of Arianism.
Nestorius believed in a two-nature Christology that split Jesus Christ into two distinct natures: one divine and one human. He believed that Mary was the mother of the human Jesus, but not of the divine Jesus. This two-nature Christology was a popular belief in Antioch at the time, and was based on the teachings of two Cilician priests, Diodorus of Tarsus and Theodore of Mopsuestia.
Nestorius' first critics were his own clergy, and then the Patriarch of Alexandria St. Cyril. St. Cyril attacked Nestorianism in a letter to all the monks of Egypt, and then in a series of personal letters to Nestorius. In his third letter to Nestorius in 430, St. Cyril demanded that Nestorius condemn the theology of two natures and agree that the divine nature of Jesus suffered in the flesh and not just in the human Jesus. The Patriarch wrote a denunciation of the doctrine called “Contra Nestorium,” which he sent, along with selected sermons by Nestorius, to the pope for official review. The pope then summoned Nestorius to recant his views within 10 days.
Council of Ephesus
Nestorianism was denounced at the Council of Ephesus in 431, and Nestorius was excommunicated because the council accused him of teaching that Christ was only a human being. The council was confirmed by Pope Sixtus III, but the new pope committed himself to restoring peace between the partisans on this issue during his reign from 432 to his death in 440.
In 435 Nestorius was exiled to Egypt. Some Syrian bishops who were supporters of Nestorianism formed a separate Christian church to continue the teachings of Nestorius. They subtracted five books from the traditional New Testament canon, for a total of 22 books.