How should one celebrate the receiving of the Torah? The Talmud (Pesachim 68b) quotes a seemingly strange argument as to how to properly celebrate Yom Tov in general, and Shavuot in particular. "Rav Eliezer says, a person on Yom Tov either eats and drinks or sits and learns". One may choose how to celebrate, but that choice must be performed with full dedication. Apparently, he felt that trying to celebrate Yom Tov in two different ways gives neither its proper due.
The opinion of Rav Yehoshua, which is the accepted one in Jewish law, is that one should "split the day, half for eating and drinking and half for the study hall". Yom Tov celebrates the combination and culmination of G-d and man acting together in history, and is thus divided between G-dly activities and the merely human. The Talmud then continues with the rather startling statement that on Shavuot, all agree that one must celebrate by eating and drinking, as it is the day we received the Torah.
On the face of it, one would have thought the exact opposite. Should not the day we received our spiritual heritage be marked by studying Torah? This reasoning is the basis for the custom of many to stay up the entire night of Shavuot, engrossed in the study of Torah. Why, then, this emphasis on eating? It is especially strange when one considers that when he was receiving the Torah from G-d, Moshe "remained on the mountain forty days and forty nights; bread I did not eat and water I did not drink" (Devarim 9:9).
The Beit Halevi (Rav Yosef Dov HaLevi Soloveitchik, the "founder" of the Soloveitchik "dynasty") explains that our insistence on food for Shavuot is rooted in a midrashic passage relating to Matan Torah. The Talmud (Shabbat 88b) relates that, as Moshe ascended to Sinai, the angels pleaded with G-d not to give the Torah to man. After all, they argued, man is a deceitful sinner; and it would be better to "bury" the Torah than to give it to people who will often ignore its teachings. The Talmud records that the Almighty made Moshe answer this cogent argument of the angels; apparently, only a good rebuttal would allow the risk of entrusting the Torah to human beings.
Moshe fired off a series of responses pointing out the many mitzvoth that relate to our physical existence. Torah is not meant for the spiritual elite; were that the case, it could have remained in heaven. Rather, Torah is meant for those who live in the physical world, teaching man how to turn eating into a seudat mitzvah, or marriage into an act of holiness. Torah is meant to refine our character, challenging us to live up to our potential. It is precisely because man is a natural sinner that we need Torah.
What better way to demonstrate this than by taking the most animalistic of acts, eating, and turning our meals into vehicles for the service of G-d and man? Eating allows us to show gratitude to our Creator, and to share our bounty with the less fortunate, including the animals that must be fed before we sit down to eat. It teaches man discipline and restraint. It helps to form friendships; it preserves the integrity of the Jewish community by forcing us to eat amongst those who share our laws. The custom to eat dairy products on Shavuot, the Bait Halevi explains, originated to demonstrate our fidelity to these laws of kashrut. Yom Tov requires one to eat a meat meal, but we purposely eat a separate dairy meal first, demonstrating our acceptance of the laws of kashrut.
It is not only on Shavuot that we celebrate the receiving of the Torah. The Torah that we have today was actually given on Yom Kippur, the covenant established on Shavuot having been broken by the building of the golden calf. While the seriousness of Yom Kippur precludes eating, Jewish law actually requires one to eat on the 9th of Tishrei; receiving the Torah requires food. Yom Kippur is the date of forgiveness, of pleading before G-d that we will do our best to do better. Moshe Rabbeinu's efforts on the first Yom Kippur enabled G-d to re-establish the covenant with us, and the Torah was received anew. These two motifs, repentance and acceptance of the Torah, require two modes of observance; fasting and feasting.
Approximately 900 years later on Purim, the Jewish people reaccepted the Torah, a Torah that would be centred in the Diaspora. The Sages would guide us now, as the period of prophecy had come to an end. The Midrash Tanchuma goes so far as to claim that at Sinai, the Jewish people accepted only the written Torah, and that it was only at Purim that the Jewish people willingly accepted the Oral Law. This re-acceptance of Torah requires eating and drinking, something we are required to do in abundance on Purim. And there, too, we have a fast day right next to the celebration, reminding us of the real threat faced by the Jewish people. It was this threat that led to national repentance, highlighted by a three-day fast on Pesach of that year, as we reaffirmed what we received at Sinai.
Torah is a wonderful gift from G-d to man. It allows us, even obligates us, to enjoy the physical world before us. Torah also demands that we seek out G-d, and that we reflect on our shortcomings; a process that, at times, requires withdrawal from the physical pleasures of this world. On Shavuot, the Jewish people—if only for a few, fleeting moments—reached such spiritual heights that there was no need for fasting. It is the day of pure celebration.