Jamieson, Fausset and Brown on Leviticus 15:31-33

31-33. Thus shall ye separate the children of Israel from their uncleanness--The divine wisdom was manifested in inspiring the Israelites with a profound reverence for holy things; and nothing was more suited to this purpose than to debar from the tabernacle all who were polluted by any kind of uncleanness, ceremonial as well as natural, mental as well as physical. The better to mark out that people as His family, His servants and priests, dwelling in the camp as in a holy place, consecrated by His presence and His tabernacle, He required of them complete purity, and did not allow them to come before Him when defiled, even by involuntary or secret impurities, as a want of respect due to His majesty. And when we bear in mind that God was training a people to live in His presence in some measure as priests devoted to His service, we shall not consider these rules for the maintenance of personal purity either too stringent or too minute (1Th 4:4).