Concise Bible Dictionary:

Ceremonial uncleanness had a large place in the Jewish ritual (Lev. 5:33Or if he touch the uncleanness of man, whatsoever uncleanness it be that a man shall be defiled withal, and it be hid from him; when he knoweth of it, then he shall be guilty. (Leviticus 5:3)). It demanded separation from the camp for a time, and in many cases an offering must be brought before there could be restoration. It is typical of the moral uncleanness that separates from communion with God and the assembly.