What does "cleanliness is next to godliness" mean?

Being clean is a sign of spiritual purity or goodness, as in Don't forget to wash your ears—cleanliness is next to godliness. This phrase was first recorded in a sermon by John Wesley in 1778, but the idea is ancient, found in Babylonian and Hebrew religious tracts. It is still invoked, often as an admonition to wash or clean up.