One of the possibilities is the following. In the laws of kashrut, it is prohibited to mix milk and meat foods. The prohibition comes three times in the Torah, so that the separation of the two categories of food is a crucial sign of Jewish observance. Yet milk is permitted on its own, as is meat (provided of course it is kosher), but what is not permitted is their mixture.
The Torah portion of No’ach, with its Seven Laws of the Sons of Noah, tells us that we may not consume meat that is torn from the body of a living animal (Ever Min HaChai). Meat therefore is only allowed if the animal has been properly slaughtered (using the laws of shechitah). Milk, on the other hand, comes by definition from a living animal.
In case one thought that the rule against meat from a living animal also entailed not consuming milk from a living animal, the Jewish tradition specially ordained an occasion – Shavu’ot – which features and celebrates the eating of milk products.