Rashi on Deuteronomy 14:21/רש"י על דברים י״ד:כ״א

1לגר אשר בשעריך [YE SHALL NOT EAT ANY CARRION: THOU SHALT GIVE IT] UNTO THE STRANGER THAT IS IN THY GATES — i.e. unto a stranger that is a sojourner (גר תושב) — one who has undertaken not to worship idols (i.e. one who has been converted to the fundamental tenet of Judaism) but who eats carrion (does not obey the other teachings of the Torah) (Sifrei Devarim 104:2; cf. Rashi on Leviticus 25:35).

2כי עם קדוש אתה לה׳ FOR THOU ART AN HOLY PEOPLE UNTO THE LORD — This implies: show yourself holy (abstinent) in respect to things which are permitted to you — i.e. things that are actually permitted but which some treat as forbidden you should not treat as permissible in their presence (Sifrei Devarim 104:7).

3לא תבשל גדי THOU SHALT NOT SEETHE A KID [IN ITS MOTHER’S MILK] — Three times the prohibition of seething meat in milk is mentioned in the Torah (here, and in Exodus 23:19 and Exodus 34:26) and each time in the form: “thou shalt not seethe a kid” thus excluding three species: a wild beast, fowls and unclean beasts from the prohibition (Sifrei Devarim 104:8; Chullin 113a).