Washed Feet

So we were at Maundy Thursday service, and the reading was about the feet washing. Jesus said to St. Peter that one who is already clean only needs to wash his feet. This got me thinking about what St. Paul said about committing the sin that he didn't want to do. If sin is perpetual, but we are dead to sin through Jesus, then maybe we only need our feet cleaned when we stumble because we are already clean....