The Nestorians are followers of Nestorius (c. 386–451 AD), who was Archbishop of Constantinople. Nestorianism is based on the belief put forth by Nestorius that emphasized the disunity of the human and divine natures of Christ. According to the Nestorians, the nature of Christ is divided equally between His divine nature and His human nature, but the two are distinct and separate. This idea is not scriptural, however, and goes against orthodox Christian doctrine of the hypostatic union, which states that Christ’s one nature was fully God and fully man. God the Son, Jesus Christ, took on a human nature, yet remained fully God at the same time. Jesus always had been God (John 8:58, 10:30), but at the incarnation Jesus became a human being (John 1:14).
In the first few centuries of the church, a great debate arose: what is the exact nature of Christ? How can a being be completely divine and completely human? In the West, the Roman Catholic Church decreed Jesus to be “two natures in one person,” and went on to other things. In the East, the definition of Christ’s nature was as much about politics as it was about religion, and the discussion went on far longer.
The Alexandrines, so named because the political loyalties of most who held the view were Alexandrian, were “monophysites.” They insisted that Jesus was, above all, divine. He was the teacher of divine truth and, in order to have had that truth, must have been primarily divine. To emphasize His humanity over His deity led to unthinkable assertions like “God got tired, injured, hungry, thirsty, and then died.” Apollinaris of Laodicea summarized the thought by saying the Word of God took the place of a rational soul so that a human body could preach the truth of God; the body was a mouthpiece.
The Antiochenes from Antioch thought this was ridiculous. A sacrifice that was not fully human could not redeem humans. Antiochenes were “dyophysites.” The Godhead dwelt in Jesus, no doubt, but not in any way that undermined His humanity. Jesus’ two natures were distinct from one another—although no one could precisely explain what that meant.
When Constantine had moved the political capital from Rome to Byzantium (later Constantinople), the church of the west centralized into the religious and political power of the Roman Catholic Church. The church of the east didn’t have that chance. They had several important churches spread throughout the region, each led by their own bishops. Alexandria and Antioch were two of the oldest and most important, but the church in Constantinople was considered as close to Rome as the East had. The clergy of Alexandria and Antioch constantly fought over the bishopric in Constantinople in hopes of uniting the scattered churches into a regional power house.
In 428 A.D., Nestorius became patriarch of Constantinople. He was from Antioch, and his theological (and political) leanings became clear when he declared Mary to be Christotokos, or “bearer of Christ,” not theotokos—“bearer of God.” In so doing, he said more about Jesus than Mary. He said that, above all else, the humanity of Jesus must be emphasized, His nature firmly divided, and that He was comprised of “two natures and two persons.” The human nature and person were born of Mary. The divine were of God.
The Bishop of Alexandria, among others, didn’t agree. He and his supporters marched into Constantinople and held a trial that relieved Nestorius of his position. Shortly after, Nestorius’s supporters finally arrived and held a smaller trial that convicted the Bishop of Alexandria. After much theological debate and political wrangling, Nestorius was exiled back to Antioch.
The Alexandrians exerted more pressure on the Antiochenes. The Antiochenes were forced to leave Antioch; Nestorius lived out his days in Egypt. But many of the Antiochenes fled east into Persia, where they were called “Nestorians” whether they had politically supported Nestorius or not.
The church already in Persia had its own problems. The rulers in Persia were quite religiously tolerant, but politically they hated Rome and anything that came out of Rome. The church in Persia carefully explained that they were not the same church as in Rome, and the Persians alternated between persecuting them and leaving them alone. Several Nestorian theologians settled in Persia, where the Persian church heard their thoughts on the two natures of Christ and told them, “Yes, of course, we’ve believed that all along.” So Nestorians were readily absorbed into the local church.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.