The distinction that the Israelites drew between clean and unclean had a great effect upon the whole of their religious and social life. It applied in the first place to food. Certain animals, birds, and fishes were regarded as clean and might be eaten, while others were unclean and were forbidden. See Lev. 11; Deut. 14:3–20. The flesh of any animal dying of itself or torn by wild animals was also forbidden (Ex. 22:31; Lev. 17:15; 22:8; Deut. 14:21). No Israelite might eat blood, which was regarded as containing the life; it had to be poured out and covered up (Gen. 9:4; Lev. 17:10–14; 19:26; Deut. 12:16, 23–25; 15:23). Fat also was forbidden; it belonged to God (Lev. 7:22–27).
For seven or fourteen days after the birth of a child the mother was unclean (Lev. 12). Uncleanness also resulted from the touch of a dead body (Lev. 11:8; 21:1–4, 11; 22:4–7; Deut. 21:22). The leper was unclean and communicated uncleanness to everything he touched (Lev. 13:1–46; 14). In New Testament times, to enter the house of a Gentile or to eat food with him involved uncleanness (John 18:28; Acts 10:28; 11:23). So long as a person was unclean he was cut off from the congregation. In ordinary cases of uncleanness it was sufficient to remain in seclusion till the evening and then to wash the body. In certain cases a sin offering was necessary.
Uncleanness referred to being ceremonially or ritually unclean and should not be taken to mean that the touching of a dead body or the bearing of children was morally evil. These regulations (except the prohibition against blood, which was given as early as Noah’s day) were introduced in the law of carnal commandments (of performances and ordinances) of the law of Moses; being fulfilled by the Atonement of Jesus Christ, they are no longer required of the believers. See Mark 7:15–23; Acts 10:9–16, 28; 15:29; 1 Tim. 4:4; 2 Ne. 25:24–27; Mosiah 13:29–32.