Cleanliness is next to godliness

There may be something to the phrase, "Cleanliness is next to godliness." In this morning's reading God gave the Israelites instructions on mildew, skin diseases and discharges. These people were unclean until they went through the cleansing period and ritual and it was a priest that had to inspect them and atone for them. Why a priest? I think sickness and uncleanliness is also a spiritual thing. Lev 15:31 says, "You must keep the Israelites separate from things that make them unclean, so they will not die in their uncleanness for defiling my dwelling place (tabernacle), which is among them."