The desire to be clean should from from the same desire to have right judgements. "A pure mind is thus one that makes right judgements, for that kind of mind alone can escape confusions and pollutions in its acts. We should endeavour as far as possible to achieve something similar with regard to the body too." (v. 8-9, p. 270)
The body, therefore, is an outward representation of the inward. Correct the inward, and the outward will follow.