This The distinction of clean and unclean animals existed even before the flood, though it probably then only related to sacrifices; but at this time we find there were very particular laws enacted respecting the diet of the people, and the ceremonial uncleanness contracted by touching the carcases of unclean animals. The reasons for the enactment of these laws seem to be:

1. As a test of obedience, and to teach the Israelites habits of self-denial, and the government of their appetites.

2. To keep them distinct from other nations, and consequently from their idolatrous usages, by throwing hindrances in the way of their social intercourse; for these distinctions were applicable both to persons and things. The Canaanites not only ate the animals prohibited by Moses, which we usually eat, but others also, among which dogs were one. Besides, many of those declared unclean were sacred among the heathen, and sacrificed to their gods.

3. Because those prohibited were innutritive and unwholesome; as the swine, the flesh of which being strong and difficult to digest, affords a very gross aliment, and produces, especially in hot climates, cutaneous, scrophulous, and scorbutic disorders, as the itch, leprosy, etc.

Leviticus 7:37 This is the law of the burnt offering, of the meat offering, and of the sin offering, and of the trespass offering...

Leviticus 14:54 This is the law for all manner of plague of leprosy, and scale,

Leviticus 15:32 This is the law of him that has an issue, and of him whose seed goes from him, and is defiled therewith;

Ezekiel 43:12 This is the law of the house; On the top of the mountain the whole limit thereof round about shall be most holy. Behold...