Deuteronomy 14:21

(1) To the stranger within your gates -- This is the ger toshav who takes it upon himself not to engage in the worship of other gods, and who eats carcasses.

You shall not eat of anything that is unclean through the manner of its death; you may give it to the uncircumcised stranger who is in your cities to eat it, or sell it to a son of the Gentiles; for you are a holy people before the Lord your God. It shall not be lawful for you to boil, much less to eat, flesh with milk when both are mixed together.

you must not eat anything that died by itself whether a bird, or a beast.

to the resident alien who is within your gates and has not converted to Judaism.

The person to whom one sells it may either be a stranger who does not dwell in the land, or he may have the status that I have explained [see comment on Exodus 22: 20]. Because this passage concerns meat, it is connected to the passage you must not cook a kid…, as I have previously explained [comment on Exodus 23: 19 ; the reference is to an earlier commentary on Exodus, known as the Perush Haqqaṣar — Translator].

FOR THOU ART A HOLY PEOPLE UNTO THE ETERNAL THY G-D. The purport thereof is connected with [the following prohibition], Thou shalt not seethe a kid in its mother’s milk. Although it is not an abhorrent food [for both meat and milk are permitted separately] He prohibited it because we are to be holy in [choice of] foods — or because we [ourselves] are holy — that we not become a cruel people that is not compassionate by milking the mother and extracting its milk to seethe therein its kid. And although any meat [cooked] in milk is included in this prohibition [even though it is not its own mother’s milk, a situation without apparent cruelty, nevertheless it is forbidden] because any nursing animal is called “mother” and any suckling offspring is called “kid,” and if they are together in the process of cooking there is [an element of] cruelty in all [cases whether a kid in its own mother’s milk or not].
Now, Rashi wrote: “Thou shalt not seethe a kid in its mother’s milk. This is stated three times in order to exclude a wild beast, fowls, (clean wild beast) or fowl with milk is forbidden though by the Rabbis (Yoreh Deiah 57:3). and unclean animals” [from this prohibition]. This interpretation is derived from the Scriptural use of the term kid [an expression that does not apply to any of the excluded categories]. However, the [thrice repeated] prohibition itself [teaches the following:] one forbids eating [meat cooked with milk], one forbids deriving benefit from it, and one forbids cooking it. And so did the Rabbi [Rashi] write in the section of And these are the ordinances.

לא תאכלו כל נבלה, even of the pure species which you may eat after they have been slaughtered ritually.

כי עם קדוש אתה לה' אלוקיך, even though the dead carcass is in a state of being fit for human consumption, such as by strangers in your midst or residents who have not yet converted to embrace all of Judaism’s laws. עם קדוש, ready to achieve the perfection intended for it by its Creator. (this would be slowed down or impeded by eating lower forms of living creatures, not that eating them would be harmful, objectively speaking.)

לא תבשל גדי, as is the custom among the Gentiles who believe that by doing so they will increase the numbers of their livestock (compare Moreh Nevuchim, section three 3,48)