Rabbula was born in 350 CE, at Qenneshrin, which is near Aleppo, Syria. He died in Edessa in 435 CE. He was a Greek educated civil servant. He became the Bishop of Edessa around 411 CE and was a leader in the Syrian Church.
At first Rabbula supported the Antiochian school of theology, but later he began to admire Cyril of Alexandria, who was the leading proponent of anti-Nestorian teachings.
Once he was made bishop of Edessa, he set about to reform the Church. He adamantly objected against pagan and Jewish influences. Rabbula also repressed Gnostic sects.
Tatian, the Syrian student of Justin Martyr, had compiled a harmony of the books of MaththiYahu, Mark, Luke and Yahuchanan. This harmony, called the Diatessaron in the Greek, and Evangelion da-Mechallete [the Good News of the Mixed], in the Syriac, was widely used in the Church of the East and the West. When Tatian began to become extreme in some of his practices, according to later historians, such as not eating meat or drinking alcohol and abstaining from marriage, another sect developed. Tatian was excommunicated from the Church of Rome and declared a heretic. The sect that developed was a puritanical Christian sect known as the Encratites ("those who exercise self-control"). Because Tatian was considered a heretic, Rabbula, nearly 300 years later, rejected the use of the Diatesseron, and in 436 CE, instructed his priests to use, in all the churches, the 4 separate Gospels.
Between 411-435 CE, Rabbula altered an already existing Aramaic (Syriac) version of the separated Gospels, the Peshitta, which included Shauls letters and Acts, to replace the Evangelion da-Mechallete Diatessaron, written by Tatian, around 173 CE. The Peshitta was written in the Estrangela script. It has the same books of what became the Greek Testament, whose canon was determined by the Church, minus the Jewish letters of II Peter, II John, III John, Jude, and the Revelations of John, which were still being debated by the Church. For the Eastern Syrian Church this was the closing of the canon. After the Council of Ephesus, in 431 CE, the East Syrians separated themselves from the Western and declared themselves Nestorians. The oldest confirmed surviving Peshitta manuscripts dates to 442.