1. Leviticus 15:18 (ESV)
  2. Exposition

Why was this so important for the Israelites?

Leviticus 15:18 (ESV)

18 If a man lies with a woman and has an emission of semen, both of them shall bathe themselves in water and be unclean until the evening.

The act of sexual intercourse may be a polemic against other cultures in the ancient Near East. Temple prostitution, for example, was common practice within sanctuaries and shrines of pagan gods. Such practices were forbidden for the Hebrews.