leviticus 22:4 What man soever of the seed of Aaron is a leper, or hath a running issue; he shall not eat of the holy things, until he be clean. And whoso toucheth any thing that is unclean by the dead, or a man whose seed goeth from him; - Free Bible Online

      4-6. wash his flesh with water--Any Israelite who had contracted a defilement of such a nature as debarred him from the enjoyment of his wonted privileges, and had been legally cleansed from the disqualifying impurity, was bound to indicate his state of recovery by the immersion of his whole person in water. Although all ceremonial impurity formed a ground of exclusion, there were degrees of impurity which entailed a longer or shorter period of excommunication, and for the removal of which different rites required to be observed according to the trivial or the malignant nature of the case. A person who came inadvertently into contact with an unclean animal was rendered unclean for a specified period; and then, at the expiry of that term, he washed, in token of his recovered purity. But a leper was unclean so long as he remained subject to that disease, and on his convalescence, he also washed, not to cleanse himself, for the water was ineffectual for that purpose, but to signify that he was clean. Not a single case is recorded of a leper being restored to communion by the use of water; it served only as an outward and visible sign that such a restoration was to be made. The Book of Leviticus abounds with examples which show that in all the ceremonial washings, as uncleanness meant loss of privileges, so baptism with water indicated a restoration to those privileges. There was no exemption; for as the unclean Israelite was exiled from the congregation, so the unclean priest was disqualified from executing his sacred functions in the sanctuary; and in the case of both, the same observance was required--a formal intimation of their being readmitted to forfeited privileges was intimated by the appointed rite of baptism. If any one neglected or refused to perform the washing, he disobeyed a positive precept, and he remained in his uncleanness; he forbore to avail himself of this privilege, and was therefore said to be "cut off" from the presence of the Lord.

JFB.