The cleansing rituals in the Old Testament served more than one purpose. Ritual cleansing mirrored the expected purity of the heart. After committing adultery with Bathsheba, David prayed: “Purge me with hyssop, and I shall be clean; wash me, and I shall be whiter than snow. […] Create in me a clean heart, O God, and put a new and right spirit within me” (Ps. 51:7, 10). The Law of Moses included cleansing regulations for men and women. Anyone having a discharge or coming in contact with someone with a discharge was unclean. Men were unclean after an emission of semen. Women were unclean during menstruation and after childbirth. And both sexes were unclean after intercourse (Lev. 12:1-8, 15:1-33).
In Christ all these regulations are lifted. The true Christian is, figuratively, washed in the blood of Jesus (Rev. 1:5-6) and made holy, “sanctified,” by the Spirit (1 Cor. 6:11). By Christ’s overflowing grace, a sinner stands clean and can therefore approach God’s throne with confidence (Heb. 4:14-16).
Another purpose of the cleansing rituals was medical. Following the law of Moses protected Israel from disease: “If you will diligently hearken to the voice of the Lord your God, and do that which is right in his eyes, and give heed to his commandments and keep all his statutes, I will put none of the diseases upon you which I put upon the Egyptians; for I am the Lord, your healer” (Exod. 15:26). The prohibition against intercourse during menstruation is a good example (Lev. 15:19-24). Having relations with a woman during her period puts her at risk for serious health problems.
Muhammad knew something about these Old Testament regulations, but he plainly had no idea why God had given them. This is the only way to explain his teaching about wiping excrement with one’s bare hand. The bacteria residing in fecal matter is very dangerous. Handling feces is an excellent way to spread disease.