Leviticus

And that ye may put difference between holy and unholy, and between unclean and clean;

Therefore thus saith the Lord, If thou return, then will I bring thee again, and thou shalt stand before me: and if thou take forth the precious from the vile, thou shalt be as my mouth: let them return unto thee; but return not thou unto them.

And they shall teach my people the difference between the holy and profane, and cause them to discern between the unclean and the clean.

Take heed in the plague of leprosy, that thou observe diligently, and do according to all that the priests the Levites shall teach you: as I commanded them, so ye shall observe to do.

This shall be the law of the leper in the day of his cleansing: He shall be brought unto the priest: