Rebbi — Rabbi Yehudah HaNasi — examines one of the most famous dietary laws in the Torah: "You shall not cook a kid in its mother's milk" (Exodus 23:19). This prohibition appears three times in the Torah, and the rabbis derive three separate prohibitions from it — against cooking, eating, and deriving benefit from the mixture of meat and milk. Rebbi's analysis focuses on the third: the prohibition against deriving any benefit whatsoever.
His proof comes from the juxtaposition of verses in Deuteronomy. The Torah states: "You may give it to the stranger in your gates to eat, or sell it to the gentile" (Deuteronomy 14:21). This refers to an animal that died naturally — neveilah — which a Jew may not eat but may sell to a non-Jew. Immediately after this permission, the Torah adds: "You shall not cook a kid in its mother's milk."
Rebbi reads the juxtaposition as intentional. Scripture is saying: this neveilah you may sell. But meat cooked in milk? If you have already cooked it, you may not sell it. You may not give it away. You may not derive any economic benefit from it at all.
The legal consequence is sweeping. Unlike neveilah, which retains commercial value even though Jews cannot eat it, meat cooked in milk becomes worthless in every sense. It cannot be consumed, traded, sold, or used for any purpose. The Mekhilta derives from Rebbi's reading that this particular prohibition extends beyond the mouth and into the marketplace — a total ban that encompasses every possible form of benefit a person might extract from the forbidden mixture.