One of the roles of bishops, and the purpose of many Christian writings, was to refute heresies . The earliest of these were generally Christological in nature, that is, they denied either Christ's (eternal) divinity or humanity. For example, Docetism held that Jesus' humanity was merely an illusion, thus denying the incarnation; whereas Arianism held that Jesus was not eternally divine.   Many groups were dualistic, maintaining that reality was composed into two radically opposing parts: matter, usually seen as evil, and spirit, seen as good. Orthodox Christianity, on the other hand, held that both the material and spiritual worlds were created by God and were therefore both good, and that this was represented in the unified divine and human natures of Christ.