Leviticus 15:16
And if any man’s seed of copulation go out from him, then he shall wash all his flesh in water, and be unclean until the even. And if any man’s seed of copulation go out from him, then he shall wash all his flesh in water, and be unclean until the even.
After a seminal emission a man must wash all his flesh in water and remain unclean until evening, as a rule of individual purity. The requirement belongs to Israel's laws of bodily cleansing that regulate ceremonial uncleanness, standing with the chapter's instructions about discharges and leprosy and requiring cleansing before a person is counted clean. Its purity requirements resemble laws practiced by the Zulus.
The chapter is a system of simple cleanliness and sanitation intended to prevent the spread of disease, in which being unclean until evening means separation from others for the rest of the day so that air and sunshine can complete disinfection. The physical uncleanness it describes had to be removed before the sanctuary's cleansing with blood. In its setting, leprosy is a fitting type of sin.
The chapter is among God's mighty object-lessons emphasizing the exceeding sinfulness of sin everywhere. Its regulations gain new life and blessing when read as pointing forward to Jesus Christ as the Lamb of God who takes away the sin of the world. It is part of the Levitical sanctuary service whose yearly cycle typified Christ's priestly ministry. Its ancient cleansing instruction serves as a precedent for health reform and for preparing the body as a clean dwelling place for God's Spirit.