The pluralism of early Christianity in regional faith and praxis, as well as the shifting lines of authority within the first and second centuries, make it difficult to draw the sharp boundaries required to exclude a particular opinion or group as heretical. In Against Heresies, Irenaeus says that his predecessors were unable to refute the Gnostics because they had inadequate knowledge of Gnostic systems and because the Gnostics appeared to say the same things as other Christians. Christian Gnostics of the second century claimed to have the esoteric, spiritual interpretation of Christian scriptures, beliefs, and sacraments. Their orthodox opponents sought to prove that such persons were not Christians on the grounds that Gnostic rites were occasions of immoral behavior, that their myths and doctrines were absurd, and that their intentions were destructive to true worship of God. In short, it...