Leviticus 11:7,8

And the swine— The aversion of the Jews to this animal, is universally known; it is generally considered as an emblem of impurity, but was most probably forbidden chiefly on account of its tendency to breed the leprosy: hence the Jews had a proverb, that of ten measures of leprosy which descended into the world, the swine took nine to themselves. The swine, says Dr. James, is the only animal in the creation subject to the leprosy, and also something very like what we call the king's evil, called in Latin scrophula, from scropha, a sow: as this disease is in Greek called χοιρας, from χοιρος, a swine. The measles is another contagious disease with which this animal is often infected; insomuch that it has passed into a proverb, as we learn from Juvenal, who calls it porrigo: in this distemper all the fleshly parts are full of innumerable small, round, white, hard substances, somewhat like hailstones. Hence, it must be plain to every reasonable observer, that the flesh of this animal, as an aliment, must be highly improper for a people so subject to leprosies as the Jews appear to have been, and who were inhabitants of a warm climate, which renders every thing more inclinable to putrefaction. It was, no doubt, for these reasons, that various other nations, inhabiting warm climates, had the same aversion to swine's flesh with the Jews. The Egyptians, we are informed, had it in great abhorrence, (see Genesis 46:34.) and the Arabians, Pliny tells us, carried their aversion to swine so far, that they would not suffer them to live among them; an antipathy, which subsists to this day among the Arabs, Moors, Tartars, and others; and which, as we lean from Dampier's Voyages, chap. 12 is propagated by the Mahometans into distant countries, particularly one of the Philippine Islands, where, if any person do but touch one of these creatures, he is not permitted to come into any body's house for several days after. See Spencer de Legibus Heb. lib. i. c. vii. sect. iv.

Note; 1. God's people must always be separated from the world. Though these ceremonial distinctions have ceased, yet the table of the godly man and the profane will afford as great a difference still; not only in the temperance of the one and the luxury of the other, but also in the prayer which consecrates the one, and the impious neglect of it which profanes the other. 2. From the beasts which answered but half the description, being still unclean, we may observe, that those who with some marks of the children of God, carry evident proofs of the want of others, are only almost-christians, and will as surely perish, unless altogether such, as they who make no pretences to religion.

See commentary on Leviticus 11:4