Shavuot
Shavuot, the Wheat Harvest and Receiving Torah
Both Pesach and Shavuot were originally agricultural festivals. Pesach marked the barley harvest, the cutting of the omer (barley sheaf); and Shavuot marked the wheat harvest.
The correct time to cut wheat is fifty days after the barley is ripe. Therefore it was natural to count seven weeks of seven days, 49 days from the time of the barley harvest to the wheat harvest. We call this tradition the Counting of the Omer. Shavuot means Weeks.
The Torah refers to Shavuot only as the wheat harvest and the time for bringing the choicest produce, the Bikkurim , to the Temple. The Torah does not provide a specific date for the wheat harvest, simply noting that it takes place 50 days after Pesach. Like Sukkot and Pesach, Shavuot was one of the Shalosh Regalim, the Three Pilgrimage Festivals.
After the destruction of the Temple in 70 C.E., our sages infused new meaning into the holiday of Shavuot by making it the anniversary of our acceptance of the Torah at Mount Sinai. From Chag HaBikkurim (the Festival of First Fruits), Shavuot became Zeman Matan Torah, the Season of Giving the Torah. Our sages declared that Shavuot was to be celebrated on the 6th of Sivan, although there was a Talmudic argument about the actual date of our Receiving Torah. Traditional Jews living outside the Land of Israel celebrate Shavuot on both the 6th and 7th of Sivan.
As a reliving of our experience at Mount Sinai, many Jews today stay up all night on Shavuot studying the Torah. According to our tradition, the Hebrews at Mount Sinai also didn't sleep the night after they received the Torah. Moreover, since we personally relive the acceptance of Torah each year on Shavuot, it is necessary for us to review the contract.
The tradition of staying up all night on Shavuot, called Tikkun Leil Shavuot, was introduced by Joseph Karo. It became popular first in Tzfat, the site of Lurianic Kabbalah. It has been suggested that the creation of a variety of all-night Kabbalistic rituals in Tzfat and their spread to other European Jewish communities was directly affected by the introduction of coffee into those communities.
We read the Ten Commandments found in Exodus 20 as the Torah portion for Shavuot because that describes our acceptance of Torah. Akdamut, a long poem praising God and thanking the Divine for giving us the Torah, is also traditionally read.
We read the Book of Ruth on Shavuot for three reasons. First, it describes the barley harvest, which takes place between Pesach and Shavuot. Second, it describes Ruth's insistence that she stay with Naomi: "Wherever you go, I will go; where you lodge, I will lodge; your people will be my people; and your God, my God."
Since Shavuot recreates our acceptance of the Torah at Mount Sinai, our sages connected Ruth's acceptance of the Jewish people to that holiday as well.
Finally, Shavuot is the traditional anniversary of King David's death. Since David was the great-grandson of Ruth, our sages felt it was appropriate to read her story on his Yahrzeit.
It has become a custom to eat only dairy products on Shavuot. Ashkenazic Jews specifically eat blintzes. A variety of reasons are offered for this custom. The most frequently quoted reason is based on the verse in Song of Songs 4:11: "Honey and milk shall be under your tongue." Our sages assumed that this referred to Torah; thus milk products became a symbol of Torah.
Another explanation notes that Torah contains the laws dealing with the eating of meat. Until Torah was received, the Hebrews didn't know what meat products were permitted and the rules weren't yet binding on them. From the moment they received Torah, however, the laws contained therein became obligatory. Since they were going to eat on the day they received Torah, they had to eat foods that they were sure met the new contract. Therefore, they stayed away from meat products and ate only dairy foods.
Historically, during the wheat harvest it was unlikely that people would take the time to prepare heavy meals. Therefore, during Shavuot the workers probably ate light meals, relying on dairy products.