“How was a believer to tell true Christians from the false ones?
Orthodox and gnostic Christians offered different answers, as each
group attempted to define the church in ways that excluded the other. Gnostic Christians, claiming to represent only “the few,” pointed to qualitative criteria.
In protest against the majority, they insisted that baptism did not make a Christian: according to the Gospel of Philip, many people “go down into the water and come up without having received anything,” and still they claimed to be Christians.
Nor did the profession of the creed, or even martyrdom, count as evidence: “anyone can do these things.” Above all, they refused to identify the church with the actual visible community that, they warned, often only imitated it. Instead, quoting a saying of Jesus (“By their fruits you shall know them”) they required evidence of spiritual maturity to demonstrate that a person belonged to the true church.”
Elaine Pagels, The Gnostic Gospels, Vintage Books, 1989, p. 102-4