There are a variety of explanations regarding the tradition to enjoy dairy foods on Shavuot. Perhaps the most familiar idea is that since the laws of kashrut had been given at the revelation at Mount Sinai, when the Jewish people returned to their homes they were unable to eat meat as it would now require shechita (kosher slaughter), the removal of the sciatic nerve and the forbidden fats (porging) and the removal of blood through salting. Their vessels would also have to be kashered (purged) having been used for non-kosher meat. Consequently, until these requirements were met, only dairy foods could be eaten.
Yet there are other explanations which relate the tradition to eat dairy products more directly to the character of Shavuot being zman matan Torateinu, the time of the giving of our Torah.
The Jewish mystical tradition relates milk and meat to the two the meta-physical concepts of chessed (loving-kindness) and din (judgement). Many kabbalistic sources including Rabbi Yaakov Tzvi Yalish (d. 1825) explain that the reason we may not mix meat and milk is together is that the admixture of chessed and din would be spiritually damaging to us (Kehillas Yaakov).
The link between the two concepts can be explained in the following way. Milk is made by the mother and given freely to nourish her child. The production of milk is a pure act of chessed on the mother’s part while the child is completely dependent on the supply of milk for its survival.
Meat on the other hand must be produced by the slaughter of an animal. Its death represents the ultimate judgement which corresponds to din.
The Gemara (Eruvin 54b) expands on the analogy by citing a verse in Proverbs (5:9) which compares the study of Torah to a suckling child. Once the child is able to suckle, its mother will continue to make milk. As soon as the child stops, the milk dries up. The Gemara explains that when someone engages in learning Torah, they will always find nourishment and spiritual sustenance.
If we carry the analogy further, it is interesting to note that milk is produced by small sacs in the mammary glands called alveoli which extract proteins, sugars and fat from the mother’s blood. The levels of these nutrients are controlled to provide the most appropriate mixture at each stage of the baby’s development. The initial milk (colostrum) is high in protein and low in fat so that is easily digested by the newborn but as the baby grows, the fat content increases to help the baby gain weight.
The analogy exposes perhaps the most beautiful aspect of learning Torah. The same Torah which teaches and nourishes the minds of young children is also studied by the greatest scholars and rabbis. From beginner to expert, the study Torah always has the power to inspire and stimulate. The lesson of milk on Shavuot enlightens us to the greatest act of chessed which G-d bestowed upon his people: the potential for growth by means of the most inclusive and yet comprehensive didactic system ever.