Its story
'Gnosticism' is a modern label (17th century) for a varied set of 2nd- and 3rd-century groups that gave central place to gnōsis, revealed knowledge about humanity's divine origin. Many of these systems described a supreme, unknowable God, a series of divine emanations (aeons), and a fall that produced a lower creator, the demiurge, responsible for the material world. Some people were thought to carry a divine spark; Christ came to awaken it and lead it back to its source.
Well-known teachers include Basilides in Alexandria, Valentinus (active in Rome c. 136–160) and his disciples Ptolemy and Heracleon, along with groups modern scholars call 'Sethian'. They were not one church: many Valentinians, for instance, took part in ordinary Christian congregations and saw themselves as more advanced Christians rather than a separate body.
Until the twentieth century nearly everything known about them came from opponents, above all Irenaeus of Lyon, whose Against Heresies (c. 180) answers with three arguments: the 'rule of faith' held in all the churches, the succession of bishops from the apostles as a guarantee of public (not secret) teaching, and the fourfold Gospel. Irenaeus also insists that the Creator and the Father of Jesus Christ are the same God, and on the goodness of creation and the resurrection of the flesh. Hippolytus of Rome and Tertullian carried the polemic further.
In 1945 a library of 4th-century Coptic codices was found at Nag Hammadi, Egypt, including the Gospel of Thomas, the Gospel of Truth and the Apocryphon of John. These texts let readers hear such groups in their own words and show more diversity than the Fathers described. Some scholars (Michael Williams, Karen King) even question whether 'Gnosticism' is a useful category. How these groups relate to earliest Christianity remains a matter of scholarly debate.