They went out from us, but they didn't belong to us; for if they had belonged to us, they would have continued with us. But they left, that they might be revealed that none of them belong to us.

 The first question is easy to answer. There was only one ceremony that all Christians passed through, and that was baptism; it was, indeed, in later days the standard practice at baptism to anoint Christians with holy oil, as Tertullian tells us. 