This short injunction forms a major part of the dietary (kashrut) laws in Judaism. Even people who are otherwise lax in their observance of those laws will generally not eat meat and dairy products together (or pork, but we won't go into that).
Regardless of whether or not someone accepts the latter rabbinic interpretations as valid, a significant question still remains. What was the reasoning behind the biblical injunction?
Maimonides, in the 12th, century proposed an ingenious solution, similar to the ones he came up with for other strange prohibitions in the Bible. It was meant to counter idolatrous practices.
As for the prohibition against eating meat in milk, it is in my opinion not improbable that— in addition to this being undoubtedly very gross food and very filling— idolatry had something to do with it.
Perhaps such food was eaten at one of the ceremonies of their cult or one of their festivals
-The Guide to the Perplexed 3:48.
In 1929, archaeological discoveries at Ugarit seemed to prove that Maimonides was right.
Claude Schaeffer discovered a Canaanite religious text which read in part "t\b[h g]d\bh\lb. annh[.]bhm’at". Charles Virolleaud translated the first three words as "Cook a kid in milk."
H. L. Ginsberg picked up the ball and ran with it.
He wrote that the reason the Bible forbade cooking a kid in milk was because it had to do with pagan gods and goddesses. The ritual described in the Ugarit text
“symbolizes the suckling of the newborn gods!”
Unfortunately, Ginsberg and his followers were quite wrong about the connection between the Ugarit text and the biblical injunction.
Basically, the entire reading is wrong. There is no room for an 'h', TBH means to slaughter, not to cook, and GD is coriander.
There have been many other attempts to solve the biblical puzzle, ranging from it being a prohibition on incest, to animal cruelty prevention, to being a mere practicality.
Ethnoarchaeologist Gloria London has an intriguing theory on the reason for the prohibition. In Cyprus, observing how traditional potters work, she was approached by an old woman who told her that “you never put meat into a clay pot with milk.”
London explains that "in times when people used porous clay pots to cook, everyone avoided cooking meat in containers used for milk products."
She goes on to say that "Not only did “others” refrain from mixing meat and milk in antiquity, they do so to this day. From about 300 B.C.E. in the Septuagint (the Greek translation of the Hebrew Bible), the Hebrew word for “milk” was translated to the Greek word galaktos. To this day, traditional Cypriot potters make a goat-milking pot used by women, the galaftiri. It has an open mouth and side spout unlike jars used to process meat products. These pots are never used for meat. Nor are cooking pots ever used for dairy. The shape of the pot says it all—milk or meat. Rather than a dietary restriction limited to a single group of people, it was common practice to keep all ceramic pots used for milk versus meat separate...
Normally in antiquity, as in the Troodos Mountain villages of Cyprus to this day, meat is reserved for special occasions with family and friends. It would be terrible to ruin a fine meal with sour meat as a result of boiling it in a dairy pot. Simple logic kept dairy pots separate from pots used to cook meat. It’s possible that the Bible’s commandment to separate meat and milk boils down to good housekeeping. The straightforward, practical understanding of the Biblical passage originates in the prosaic perspective of a kitchen. It comes from those who make the pots, feed the animals, milk the goat, make the yogurt and cheese, cook the meat, and serve family, friends and community."
The theory, interesting as it is, suffers from some fatal flaws.
First of all, if this was such a commonsensical and practical matter, "good housekeeping", why would it need to be regulated? Why include it in a list of laws governing a covenant relationship? Why the specific mention of kids and mothers instead of milk and meat?
The answer seems to lie in a different direction entirely.
Philo, the Jewish Alexandrian philosopher of the 1st century CE, nailed it on the head.
The reason was to avoid mixing life and death, for it is “grossly improper that the substance which fed the living animal should be used to season or flavor it after its death.”
Jacob Milgrom expands this thought.
This prohibition is, thus, simply another instance of the emphasis on opposites characteristic of biblical ritual and practice: to separate life from death, holy from common, pure from impure, Israel from the nations. The reverence for life and Israel’s separation from the nations are ideas reflected throughout the dietary laws. For example, the reverence for life is reflected in the blood prohibition. Separating Israel from the nations is reflected in the prohibition against eating certain animals such as pig and crustaceans.
Thus the prohibition against cooking a kid in its mother’s milk conforms neatly with Israel’s overall dietary system.
The command not to boil a kid in mother’s milk is first set forth in Exodus, where the context in which it appears shows that it probably applies only to kids sacrificed on one of the Israelites’ pilgrimage festivals. By the time the command appears again in Deuteronomy, however, it is apparent that it has been transformed into something much broader, a new dietary law.
It is easy to see why this prohibition would have been so quickly integrated into the Israelites’ dietary system. It embodies two common biblical themes: reverence for life, even dumb animal life, and Israel’s separation from the nations.
This life-versus-death theory also completely and neatly elucidates the other biblical prohibitions mentioned earlier that, heretofore, have been explained as having humanitarian motives. However, the common denominator of all these prohibitions is that they prevent fusion of life and death. Thus, the life-giving process of the mother bird hatching or feeding her young should not be the occasion of their joint death (Deuteronomy 22:6). The sacrifice of the newborn may be inevitable, but not for the first week while it is constantly at the mother’s breast (Leviticus 22:27); and never should both the mother and its young be slain at the same time (Leviticus 22:28). By the token, the mother’s milk, the life-sustaining food her kid, should never become associated with its death."
Ugaritic Texts, 52:14.
H. L. Ginsberg, The Ugarit Texts, pg. 77.
Milgrom, Jacob, You Shall Not Boil a Kid in Its Mother’s Milk, Bible Review, Summer 1985, pg. 48-55.
London, Gloria, Why Milk and Meat Don't Mix, Biblical Archaeology Review, Nov/Dec 2008, 66-69.
Philo, De Virtute, 143.
Milgrom, BR, Summer 1985, pg. 48-55.