explanation is that a scribe, faced with the statement, “The man who has bathed has no need to wash,” and not recognizing that the bath was the footwashing, thought that he had to insert an exceptive phrase to show that Jesus did not mean to exclude the footwashing when he said there was no need to wash. In so doing he unwittingly provided later theologians with an even richer sacramental doctrine, for the phrase could be interpreted as a reference to the necessity of Penance after the bath of Baptism.
Page 568