Genesis 7:2 - Clarke's commentary and critical notes on the Bible

Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female. Of every clean beast - So we find the distinction between clean and unclean animals existed long before the Mosaic law. This distinction seems to have been originally designed to mark those animals which were proper for sacrifice and food, from those that were not. See Leviticus 11.