Nestorianism is the doctrine that Christ exists as two persons, the man Jesus and the divine Son of God, or Logos, rather than as two natures (True God and True Man) of one divine person. The doctrine is identified with Nestorius (c. 386–c. 451), Archbishop of Constantinople. This view of Christ was condemned at the Council of Ephesus in 431, and the conflict over this view led to the Nestorian schism, separating the Assyrian Church of the East from the Byzantine Church.
Nestorianism originated in the Church in the 5th century out of an attempt to rationally explain and understand the incarnation of the divine Logos, the Second Person of the Holy Trinity as Jesus Christ. Nestorianism taught that the human and divine essences of Christ are separate and that there are two natures, the man Jesus and the divine Logos, united in Christ. In consequence, Nestorians rejected such terminology as "God suffered" or "God was crucified", because the humanity of Christ which suffered is separate from his divinity. Likewise, they rejected the term Theotokos (Giver of birth to God/Mother of God) as a title of the Virgin Mary, suggesting instead the title Khristotokos (Giver of birth to Christ/Mother of Christ), because in their view he took only his human nature from his mother, while the divine Logos was pre-existent and external, so calling Mary "Mother of God" was misleading and potentially wrong.
The Assyrian Church of the East refused to drop support for Nestorius or to denounce him as a heretic. That church has continued to be called "Nestorian" in the West, to distinguish it from other ancient Eastern churches. However, the Church of the East does not regard its doctrine as truly Nestorian: it teaches the view of Babai the Great - Christ has two qnome (essences) that are unmingled and eternally united in one parsopa (personality). According to some interpretations, the origin of this belief is mostly historical and linguistic: for example, the Greeks had two words for 'person', which translated poorly into Syriac, and the meanings of these terms were not even quite settled during Nestorius's lifetime.
There are about 170,000 Nestorians today, mostly living in Syria, Iraq and Iran .
Nestorius (c. 386–c. 451) was a pupil of Theodore of Mopsuestia in Antioch in Syria (modern Turkey) and later became Archbishop of Constantinople. He taught that the human and divine aspects of Christ were distinct natures, not unified. He preached against the use of the title Mother of God (Theotokos) for the Virgin Mary and would only call her Mother of Christ (Christotokos). He also argued that God could not suffer on the cross, as he is omnipotent. Therefore, the human part of Christ died on the cross, but not the divine.
His opponents accused him of dividing Christ into two persons: they claimed that proposing that God the Word did not suffer and die on the cross, while Jesus the man did, or that God the Word was omniscient, while Jesus the man had limited knowledge, implied two separate persons with separate experiences.
The Council held that Christ is one person, and that the Virgin Mary is the mother of God. The condemning pronouncement of the Council resulted in the Nestorian schism and the separation of the Assyrian Church of the East from the Byzantine Church. However, even Ephesus could not settle the issue, and the Byzantine Church was soon split again over the question of whether Christ had one or two natures, leading to the Chalcedonian schism.
During the Protestant Reformation, when some groups denied the Real Presence and the communication of attributes between the two natures, they were accused of reviving the heresy of Nestorius. The same charge was levelled at the Catholics Isaac-Joseph Berruyer in the eighteenth century, and Anton Günther in the nineteenth century.
At Nisibis the school became even more famous than at Edessa. The main theological authorities of the school have always been Theodore and his teacher Diodorus of Tarsus. Unfortunately, few of their writings have survived. The writings of Nestorius himself were only added to the curriculum of the school of Edessa-Nisibis in 530, shortly before the Fifth Ecumenical Council in 553 condemned Theodore of Mopsuestia as Nestorius's predecessor.
At the end of the 6th century the school went through a theological crisis when its director Henana of Adiabene tried to replace Theodore with his own doctrine, which followed Origen. Babai the Great (551–628), who was also the unofficial head of the Church at that time and revived the Assyrian monastic movement, refuted him and in the process wrote the normative Christology of the Assyrian Church, based on Theodore of Mopsuestia.
A small sampling of Babai's work is available in English translation The Book of Union is his principal surviving work on Christology. In it he explains that Christ has two qnome (essences), which are unmingled and eternally united in one parsopa (personality). This, and not strict Nestorianism, is the teaching of the Assyrian Church. However, the Assyrian Church has continued to be called "Nestorian" in the West to distinguish it from other ancient Eastern churches, despite the fact that Babai's Christology is basically the same as that of Catholicism and Orthodoxy; the Baltimore Catechism teaches that Christ is one "person" (like Babai's parsopa) but has two "natures" (Babai's qnome).
The Assyrian Church produced many zealous missionaries, who traveled and preached throughout Persia and Central and East Asia in the seventh and eighth centuries. Also during this time many Nestorian scholars, having escaped the Byzantines, settled in Gundishapur, Persia and Muharraq in Bahrain, bringing with them many ancient Greco-Roman philosophical, scientific, and literary texts. “Nestorian” Christianity reached China by 635, and its relics can still be seen in Chinese cities such as Xi'an. The Nestorian Stele, set up on 7 January 781 at the then-capital of Chang'an (modern Xi'an), describes the introduction of Christianity into China from Persia in the reign of Taizong of Tang, and documents found at the Mogao Caves near Dunhuang further elucidate the religion. About the same time Nestorian Christianity penetrated into Mongolia, eventually reaching as far as Korea. Some historians even suggest that they made it to the shores of Japan. In AD 797 , a Japanese history, Shoku Nihongi was published. It states that in AD 736 an envoy returned to Japan from China. He brought with him a Persian physician by the name of Limitsi (or Rimitsui, 李密医), and Kohfu (皇甫), a “dignitary of the church of the Luminous Religion”. The “Luminous religion” is (Nestorian) Christianity - because Christ is “the Light of the World”. The Syrian Christians of Kerala, India may have been converted by Nestorian missionaries in the 7th century AD according to one of the two dominant theories about their origin (the other, more traditional theory is that they were converted in 52AD by St Thomas or his delegates )
The Christian community later faced persecution from Emperor Wuzong of Tang (reigned 840–846). He suppressed all foreign religions, including Buddhism and Christianity, which then declined sharply in China. A Syrian monk visiting China a few decades later described many churches in ruin.
Nestorianism was particularly active in the 12th century, being a state religion of Khitans in the times of Yelü Dashi. It was also one of the widespread religions in the empire of Genghis Khan, and several Nestorian gravestones written in Syriac survive in what is today Kyrgyzstan.
The Church experienced a significant revival during the Yuan dynasty. Marco Polo in the 1200s and other medieval Western writers indicate many Nestorian communities remaining in the Middle East, Central Asia, China and Mongolia. Rabban Bar Sauma, a Nestorian traveler from Shang-du (the "Xanadu" of Coleridge's poem, in present-day inner Mongolia), became a diplomat for the Mongol Il-Khanate of Persia to the courts of Constantinople and Rome for talks of a Franco-Mongol alliance against the Muslims at this time. However, the Nestorians clearly were not as vibrant as they had been during Tang times. The communities seem to have petered out during the Ming dynasty from lack of popular support. The legacy of the missionaries remains in the Assyrian churches still to be found in Iraq, Iran, and India.