Egyptian Christianity developed during the 1st century AD under the patriarch of Alexandria. The Copticscript was used to translate the Holy Scriptures and religious works. Strains soon appeared between the orthodox formula for the nature of Christ, which was two natures—human and divine intermingled—as set down by the councils of Nicaea in 334 and Chalcedon in 454, and the belief in Egypt of one divine nature known as Monophysitism. After failing to find a compromise, the Byzantine emperors, with the support of the Roman popes, sought to impose orthodoxy in Egypt, leading to a schism when a Coptic patriarch of Alexandria was elected in opposition to the orthodox one. Most Egyptians supported the Coptic church, and their loyalty to the emperor was weakened, facilitating the Arab conquest. This in turn led to the eventual decline of the native church, since large parts of the population eventually converted to Islam, and the Coptic languagewas replaced by Arabic. The Coptic church is more vigorous at present than it was for several centuries.
Historical Dictionary Of Ancient Egypt by Morris L. Bierbrier
Ancient Egypt. A Reference Guide. EdwART. 2011.