John Calvin Commentary Deuteronomy 14:21

"Ye shall not eat of anything that dieth of itself: thou mayest give it unto the sojourner that is within thy gates, that he may eat it; or thou mayest sell it unto a foreigner: for thou art a holy people unto Jehovah thy God. Thou shalt not boil a kid in its mother`s milk." — Deuteronomy 14:21 (ASV)

You shall not eat of anything that dies of itself.

The eating of any carcass, or of flesh torn by wild beasts, is reckoned among the causes of defilement. However, we must understand this to refer to the carcass of an animal that has died of hunger or disease, for from the nature of its death, it contracted impurity, although it was otherwise pure in itself. The purpose of the precept is gathered from the reason that is immediately added, “for you are a holy people to the Lord your God,” and from the washing that is prescribed in the passage from Leviticus.

Secondly, the same thing is commanded respecting flesh that has been torn, as previously with regard to the carcass, for the deformity of its laceration is counted as uncleanness. The holiness of the people is again mentioned, so that they may more diligently guard against defilements. Consequently, it follows that those who ate of torn flesh were contaminated.

Therefore, in the third passage, he confirms that the Jews were to abstain and were prohibited from eating a carcass or the flesh of an animal torn by beasts, so that they would not pollute themselves. It is not an objection that eating carrion and blood are prohibited here together, for we know that Moses does not always arrange his precepts in order but sometimes presents those that pertain to different categories without strict sequence. Therefore, I have thought it good to separate these two prohibitions, which have distinct purposes, and whose difference clearly appears from their different punishments. The one who eats blood will be cut off from the people, whereas the one who eats carrion must wash himself and will be unclean until the evening.

A question might again arise regarding torn or lacerated flesh. However, in my judgment, it seems plain enough from the context that flesh torn by beasts is counted among unclean meats, for the reason for the law is expressed, namely, because those who were chosen to be a holy people should keep themselves pure and uncorrupted. Nor would God command that meat intended for humans should be thrown to dogs unless it were infected with a contagion that would pollute His holy people.

Regarding the command in the first passage—to give it to a stranger or sell it to an alien so that he might eat it—this does not appear reasonable, since that would be to supply the means for sin, as if one were to offer a sword to a madman or transfer illicit goods to others. But the solution to this difficulty is easy: for the Gentiles were permitted to eat all sorts of food without distinction, since no such dietary restrictions were placed on them. The prohibition of certain meats, however, was a mark of separation between them and the chosen people of God.

A more difficult question arises from an apparent contradiction, because Moses in another passage binds both the stranger and the native-born by the same law, declaring them to be equally unclean if they taste carrion. But we must bear in mind that he sometimes calls those "strangers" who, although born of heathen parents, had embraced the Law. Circumcision, therefore, connected them with God, just as if they had originated from Abraham, while there were other strangers whom uncircumcision separated from the children of Abraham as profane and excommunicated.

The sum is that whoever professes God’s name and boasts of being His people is called to cultivate holiness and to keep themselves pure from every stain.