By the second century, perhaps much earlier, Christianity was divided into two main branches - what is now known as the proto-Catholic-Orthodox branch and Gnosticism. While the proto-Catholic-Orthodox branch was disciplined and and developed a hierarchical structure, Gnosticism generally felt no need to enforce discipline among its members nor to have bishops as overseers. Gnostics were encouraged to seek direct access to God by prayer and revelation, rather than through the clergy.
Athanasius, bishop of Alexandria, sought to block anyone seeking direct access to God. In
On the Incarnation of the Word, he explained that human sin had damaged that image beyond human repair. Augustine later developed this into his understanding of "original sin". Augustine himself was a Manichaean before joining the Catholic Church.
While there was a good deal of antagonism between the two branches, there was also an interchange of religious ideas. The Gnostics were prolific authors and wrote numerous gospels and other books. The Gospel of Thomas and possibly the Gospel of John were written in the Gnostic milieu and later adopted by orthodox Christianity, with modifications to remove much of the gnostic content. The Gospel of Thomas had strong support for inclusion in the orthodox New Testament.
Gnostic Christians often attended orthodox church servoices, not only as places of worship, but also in order to recruit members to Gnosticism.