LEPROUSY IS A PUNISHMENT FOR IDOLATRY AND IMMORALITY

Midrash Rabbah - Numbers 7:10

We have likewise learnt: Exile comes into the world for idolatry, for immorality, for bloodshed, and for neglect of the septennial rest of the land. ‘For idolatry.’ How so? It says, And I will destroy your high places, etc. (Leviticus 26:30), and it is written, And you will I scatter among the nations, etc. (Leviticus 26:33). Said the Omnipresent to Israel: ‘Seeing that you have a desire for idolatry, I shall on my part exile you to a place where there is idolatry;’ therefore, I will destroy your high places.’ ‘For immorality.’ How so? R. Ishmael, son of R. Jose, said: So long as Israel are sunk in immorality the Shechinah keeps away from them; as it says, That He see no immoral thing in thee, and turn away from thee (Deuteronomy 23:14).