On the contrary, It is written (Deut. 18:14):  “But thou art otherwise instructed by the Lord thy God”:  from which words we may gather that these observances were instituted by God to be a special prerogative of that people.  Therefore they are not without reason or cause.

I answer that, The Jewish people, as stated above (A. 5), were specially chosen for the worship of God, and among them the priests themselves were specially set apart for that purpose.  And just as other things that are applied to the divine worship, need to be marked in some particular way so that they be worthy of the worship of God; so too in that people’s, and especially the priests’, mode of life, there needed to be certain special things befitting the divine worship, whether spiritual or corporal.  Now the worship prescribed by the Law foreshadowed the mystery of Christ:  so that whatever they did was a figure of things pertaining to Christ, according to 1 Cor. 10:11:  “All these things happened to them in figures.”  Consequently the reasons for these observances may be taken in two ways, first according to their fittingness to the worship of God; secondly, according as they foreshadow something touching the Christian mode of life.

Reply Obj. 1:  As stated above (A. 5, ad 4, 5), the Law distinguished a twofold pollution or uncleanness; one, that of sin, whereby the soul was defiled; and another consisting in some kind of corruption, whereby the body was in some way infected.  Speaking then of the first-mentioned uncleanness, no kind of food is unclean, or can defile a man, by reason of its nature; wherefore we read (Matt. 15:11):  “Not that which goeth into the mouth defileth a man; but what cometh out of the mouth, this defileth a man”:  which words are explained (Matt. 15:17) as referring to sins.  Yet certain foods can defile the soul accidentally; in so far as man partakes of them against obedience or a vow, or from excessive concupiscence; or through their being an incentive to lust, for which reason some refrain from wine and flesh-meat.

If, however, we speak of bodily uncleanness, consisting in some kind of corruption, the flesh of certain animals is unclean, either because like the pig they feed on unclean things; or because their life is among unclean surroundings:  thus certain animals, like moles and mice and such like, live underground, whence they contract a certain unpleasant smell; or because their flesh, through being too moist or too dry, engenders corrupt humors in the human body.  Hence they were forbidden to eat the flesh of flat-footed animals, i.e. animals having an uncloven hoof, on account of their earthiness; and in like manner they were forbidden to eat the flesh of animals that have many clefts in their feet, because such are very fierce and their flesh is very dry, such as the flesh of lions and the like.  For the same reason they were forbidden to eat certain birds of prey the flesh