Why the Custom of Eating Dairy Food on Shavuot?

Shavuot is approaching quickly. In a matter of hours, Jews celebrate the moment when the Israelites received the Torah at Mount Sinai. What is interesting about this holiday is that there is not a ritual that particularly defines the holiday. With Rosh HaShanah, you have the blowing of the shofar. Yom Kippur comes with a fast. Sukkot comes with both the Four Species and the sukkah. Passover has the seder and matzah. But Shavuot, nothing......well, sort of nothing. Shavuot was one of the three festivals for which one made a pilgrimage to the Temple. We have no Temple anymore, so it would be more accurate to say that there is no biblical-era ritual that exists for Shavuot. The explanation I have heard is that there is no particular ritual because the holiday is supposed to be about Torah. The Torah is the main focus of Shavuot. Even so, there are some relatively minor rituals and traditions that have evolved, such as studying Torah all night, as well as the tradition I would like to focus on today: eating dairy food.

This tradition is mentioned in the fourteenth century in Rabbi Yitzchak Tyranu's text, Sefer HaMinhagim (although some think it was mentioned in the thirteenth century). This legalistic work does not explain the meaning or significance behind the text. Here are a few reasons for the practice that have evolved over the years:

1. Multiple sources, including R. Aharon HaCohen and R. Meir of Rothenberg, opine that we celebrate the Torah on Shavuot, and as such, there are verses in the Song of Solomon that allude to Torah: "Like honey and milk, [the Torah] lies under your tongue (Song of Solomon, 4:11)." There are some that use this verse as a basis to eat honey on Shavuot, as well as dairy products. 
2. The Chofetz Chaim suggests that the practice comes from Mount Sinai itself. At Mount Sinai, the Jews were given the laws of separating meat and dairy. With these new laws, they did not have kosher dishes. Since dairy food does not require the same extent of preparation, that is what was eaten during the first Shavuot, and we thus take on that tradition. The problem with this explanation is that the explanation came well after the practice came, which creates an anachronism. 
3. R. Yechiel Michel Epstein noted that Numbers 28:26 talks about a meat offering for Shavuot (מנחה חדשה להי בשבעתיכם). This phrase works out as an abbreviation for "from milk" (מחלב), and therefore we eat milk.
4. According to gematria (Jewish numerology), the Hebrew word for milk (חלב) adds up to 40. The 40 corresponds to the 40 days Moses spent on Mount Sinai. To commemorate that event, we eat dairy products (R. Yitzchak Lipietz; R. Menachem Mendel of Ropshitz). 
5. Milk was historically kept in simple vessels, such as clay or glass. If milk were kept in something fancy like silver or gold, it would spoil. If we go back to the metaphor that Torah is like milk, then Torah is meant for those who are humble, not for the haughty (R. Elyakum Dvorkas). 
6. At the end of Pirkei Avot, there is a list of 48 ways to acquire Torah. One of the ways on the list is through not [excessively] indulging oneself. Meat is considered an indulgence in traditional Judaism, and as such, we teach ourselves the lesson that Torah is not acquired through physical and material indulgence (R. Avraham Hershovitz). 
7. The Zohar states that each of the 365 negative mitzvahs corresponds to a day on the solar calendar. Which mitzvah corresponds to Shavuot, asks the Zohar? The mitzvah to not mix a kid with its mother's milk. In Exodus 34:26, the verse starts off by bringing the first fruits to the Temple. The verse finishes with the prohibition on mixing meat with dairy. On Shavuot, we eat two meals (one meat and one dairy) and are mindful not to mix the two together. Since two loaves are eaten for the two meals, the two loaves correspond to the offerings given on Shavuot (Rema, OC, 494:3).
8. According to the Talmud (Bechorot 6a), honey is made from the bee, and milk is a byproduct of cow. These products could be construed as non-kosher because they come from a live animal, which is a violation of one of the seven Noahide laws (FYI: neither honey nor milk are considered non-kosher). While the source of these products would be considered spiritually unclean, the end-product is considered spiritually pure. Upon receiving the Torah, milk became kosher to the Jews. This is analogized to the fact that the Torah has the ability to take something impure and render it pure (R. Shlomo Kuger). I'm not a fan of this homily for a few reasons, most notably being that the Torah does not render everything pure, and that there are still items considered non-kosher, but I digress.
9. Another reason is that it is a reminder that Moses was saved from being slaughtered by the Egyptians when he was a baby. What does Moses' infancy have to do with Shavuot? According to the Talmud (Sotah 12b), Moses' mother placed Moses in the basket of reeds and sent him along the Nile. None of the Egyptian women were able to nurse Moses. The Pharaoh's daughter found one woman, Moses' biological mother, to nurse Moses. The eating of dairy food is supposed to commemorate the miracle that took place in Moses' live on the sixth of Sivan, which is the same date on the Jewish calendar as Shavuot (Yalkut Yitzchak).
10. Another name for Mount Sinai is Mount Gav'nunim (הר גבנונים; see Psalms 68:17). The name גבנונים is etymologically similar to the Hebrew word for cheese (גבינה). More to the point, the gematria for the word גבינה adds up to 70, which alludes to the "70 faces of Torah" (Rebbe of Ostropole).
11. The Jerusalem Talmud (Chagigah 2:3) provides another reason. According to the Talmudic passage, King David passed away on Shavuot. When a king passes away, the entire community is in a mourning state, and back in those days, it meant not eating the sacrificial meat offering, which meant eating dairy only. This argument is tenuous because one does not mourn on yom tov, not to mention that this is not a widely accepted reason for the practice. 

The fact that I was able to cite so many reasons for this practice (and I'm pretty sure this doesn't even cover all of the reasons) implies that we really don't know the reason why the practice of eating dairy on Shavuot exists in the first place. On the other hand, it shouldn't matter. Why? Because one of the many beauties of Jewish tradition is that we can come up with multiple, spiritually meaningful explanations for the practice. Whichever speaks to you, may it bring you a sense of purpose as you eat your dairy meal this Shavuot.