Calvin's Commentaries, Vol. 4: Harmony of the Law, Part II, tr. by John King, [1847-50], at sacred-texts.com
19. ... Thou shalt not seethe a kid in his mother’s milk.
19. Non coques hoedum in lacte matris suae.
19. Thou shalt not seethe a kid. The threefold repetition of the command reminds us that a serious matter is spoken of, whereas it would be a light and almost frivolous one, if, as some suppose, it is merely the prohibition of a somewhat unwholesome food. But the Jews, not considering its intent, and affecting sanctity, as they do, in trifling puerilities, dare not taste of cheese together with kid, or lamb’s flesh, until they have well cleaned their teeth. I have no doubt, however, but that this prohibition relates to the sacrifices, for in the first passage quoted, it is added in connection with the offering of the first-fruits; and in the second, we read as follows: “The first of the first-fruits of thy land thou shalt bring unto the house of the Lord thy God. Nor shalt thou seethe a kid in his mother’s milk;” and so also in the third passage: “Ye shall not eat of any thing that dieth of itself, etc., for thou art an holy people unto the Lord thy God; nor shalt thou seethe a kid in his mother’s milk.” I allow indeed that Moses sometimes mixes together precepts respecting different things; but this running context shews that this precept is delivered among the ceremonies, and must therefore be reckoned to be a part of the legal service. Whence I conclude, that the people are not only interdicted from eating this sort of food, as if they were to partake of flesh steeped in blood; but that they should not pollute the sacrifices by the carnal mixture. It is however probable, that meat seasoned with milk was accounted a delicacy; but inasmuch as they might grow cruel, if they ate of a lamb or kid in its mother’s milk, God forbade to be offered to Himself, what was not allowable even in their common meals. The exposition of some, that kids were excluded from their tables until they were weaned, is not agreeable to reason; because they then begin to have a goatish flavor. But the reason is a very appropriate one, i.e., that God would not admit a monstrous thing in His sacrifices, that the flesh of the young should be cooked in its mother’s milk, and thus, as it were, in its own blood.