Three times in the Torah we find the prohibition repeated “Thou shalt not seethe a kid in its mother’s milk” (see Shemot23:19, 34:26 and Devarim 14:21). Although it appears that the Torah limits this prohibition to a specific case – a kid in its mother’s milk – nevertheless the Sages had a long-standing tradition that these passages refer to a general prohibition against cooking milk and meat together. The fact that this prohibition is repeated three times is understood as forbidding not only cooking milk and meat together, but also eating them cooked together and deriving any benefit from such a mixture.
The eighth perek (=chapter) of Masechet Hullin begins on today’s daf (=page) and its focus is on these laws. Given the enigmatic presentation of the prohibition of cooking meat and milk together, there are many issues that need to be clarified by the Sages, the most basic of which is how we define the terms “milk” and “meat.” Is all meat included? Is there a difference between meat from domesticated animals (behemot) and wild animals (hayyot)? What is the status of the meat of kosher birds, fish or insects? Similarly, is the prohibition limited to actual milk, or are other milk products forbidden, as well?
The first Mishnah teaches “every kind of meat is forbidden to be cooked in milk, except the meat of fish and of locusts; and it is also forbidden to place upon the table meat with cheese, excepting the flesh of fish and of locusts.”
This last requirement – to separate meat and milk products even if they are not being cooked together – is not part of the biblical prohibition included in the thrice repeated passage, it is a Rabbinic injunction whose purpose is to keep people from mistakenly eating them together. This applies, however, only to a table where people are eating; on the table where food is being prepared there is no such requirement.