 The purpose is to underline the character of altar priesthood (i.e., those priests with power to offer sacrifices to God) as an Aaronite privilege, and the responsibilities and dangers of their position.With sacrifice and priesthood established, chapters 11–15 instruct the lay people on purity (or cleanliness).Eating certain animals produces uncleanliness, as does giving birth; certain skin diseases (but not all) are unclean, as are certain conditions affecting walls and clothing (mildew and similar conditions); and genital discharges, including female menses and male gonorrhea, are unclean.