Story
Gnostics and their critics
Second-century arguments about the creator, the scriptures, and who may teach.
Step 1
Marcion forces a list
Marcion separated the God of the Hebrew scriptures from the Father of Jesus and published a gospel plus Paul. Other Christians answered by saying which books they read and that the creator is the Father. Whatever else canon formation is, it is partly an answer to Marcion.
Step 2
Valentinus and Basilides
Valentinus in Rome and Basilides in Alexandria taught mythic accounts of how the divine world and the material world are related. Irenaeus and others summarized them in order to refute them. Where their own texts survive, the summaries are only partly right.
Step 3
A pagan reads the same fight
Celsus, a pagan critic, already knew Christian disagreements and used them. Origen's answer preserves Celsus's arguments at length. The debate was public, not only an internal pamphlet war.