Christianity in the 6th century in the context of "Christianity in the 4th century"

The Church of the East (Classical Syriac: ܥܕܬܐ ܕܡܕܢܚܐ ʿĒḏtā d-Maḏenḥā) or the East Syriac Church, also called the Church of Seleucia-Ctesiphon, the Persian Church, the Assyrian Church, the Babylonian Church, the Chaldean Church or the Nestorian Church, is one of three major branches of Eastern Nicene Christianity that arose from the Christological controversies in the 5th century and the 6th century, alongside that of Miaphysitism (which came to be known as the Oriental Orthodox Churches) and Chalcedonian Christianity (from which Catholicism, Eastern Orthodoxy and Protestantism would arise).

Having its origins in Mesopotamia during the time of the Parthian Empire, the Church of the East developed its own unique form of Christian theology and liturgy. During the early modern period, a series of schisms gave rise to rival patriarchates, sometimes two, sometimes three. In the latter half of the 20th century, the traditionalist patriarchate of the church underwent a split into two rival patriarchates, namely the Assyrian Church of the East and the Ancient Church of the East, which continue to follow the traditional theology and liturgy of the mother church. The Chaldean Catholic Church based in Iraq and the Syro-Malabar Church in India are two Eastern Catholic churches which also claim the heritage of the Church of the East.

In the 5th century in Christianity, there were many developments which led to further fracturing of the State church of the Roman Empire. Emperor Theodosius II called two synods in Ephesus, one in 431 and one in 449, that addressed the teachings of Patriarch of Constantinople Nestorius and similar teachings. Nestorius had taught that Christ's divine and human nature were distinct persons, and hence Mary was the mother of Christ but not the mother of God. The Council rejected Nestorius' view causing many churches, centered on the School of Edessa, to a Nestorian break with the imperial church. Persecuted within the Roman Empire, many Nestorians fled to Persia and joined the Sassanid Church (the future Church of the East) thereby making it a center of Nestorianism. By the end of the 5th century, the global Christian population was estimated at 10-11 million. In 451 the Council of Chalcedon was held to clarify the issue further. The council ultimately stated that Christ's divine and human nature were separate but both part of a single entity, a viewpoint rejected by many churches who called themselves miaphysites. The resulting schism created a communion of churches, including the Armenian, Syrian, and Egyptian churches, that is today known as Oriental Orthodoxy. In spite of these schisms, however, the imperial church still came to represent the majority of Christians within the Roman Empire.

At the end of the 4th century the Roman Empire had effectively split into two states although its economy and the Church were still strongly tied. The two halves of the empire had always had cultural differences, in particular exemplified by the widespread use of the Greek language in the Eastern Empire and the more limited use of Greek in the West (Greek was used in the West but Latin was displacing it as the spoken vernacular. By the 5th century scholars in the West had begun to abandon Greek in favor of the use of Latin. The Church in Rome, in particular, began to encourage the use of Latin in the western provinces and published Jerome's Vulgate, the first authorized translation of the Bible in Latin.

Christian universalism is a school of Christian theology focused around the doctrine of universal reconciliation – the view that all human beings will ultimately be saved and restored to a right relationship with God. "Christian universalism" and "the belief or hope in the universal reconciliation through Christ" can be understood as synonyms.

The term Christian universalism was used in the Christian Intelligencer in the 1820s by Russell Streeter—a descendant of Adams Streeter who had founded one of the first Universalist Churches on September 14, 1785. Some Christian universalists claim that in Early Christianity (prior to the 6th century), this was the most common interpretation of Christianity.