Shavuot 101

and the Feast of the Harvest, of the first fruits of your work, of what you sow in the field...

On the day of the first fruits, your Feast of Weeks, when you bring an offering of new grain to the LORD, you shall observe a sacred occasion: you shall not work at your occupations.

(2) you shall take some of every first fruit of the soil, which you harvest from the land that the LORD your God is giving you, put it in a basket and go to the place where the LORD your God will choose to establish His name.

"And God spoke to Moses in the Sinai Wilderness" (Numbers 1:1). Why the Sinai Wilderness? From here the sages taught that the Torah was given through three things: fire, water, and wilderness. How do we know it was given through fire? From Exodus 19:18: "And Mount Sinai was all in smoke as God had come down upon it in fire." How do we know it was given through water? As it says in Judges 5:4, "The heavens dripped and the clouds dripped water [at Sinai]." How do we know it was given through wilderness? [As it says above,] "And God spoke to Moses in the Sinai Wilderness." And why was the Torah given through these three things? Just as [fire, water, and wilderness] are free to all the inhabitants of the world, so too are the words of Torah free to them, as it says in Isaiah 55:1, "Oh, all who are thirsty, come for water... even if you have no money." Another explanation: "And God spoke to Moses in the Sinai Wilderness" — Anyone who does not make themselves ownerless like the wilderness cannot acquire the wisdom and the Torah. Therefore it says, "the Sinai Wilderness."

The Gemara cites additional homiletic interpretations on the topic of the revelation at Sinai. The Torah says, “And Moses brought forth the people out of the camp to meet God; and they stood at the lowermost part of the mount” (Exodus 19:17). Rabbi Avdimi bar Ḥama bar Ḥasa said: the Jewish people actually stood beneath the mountain, and the verse teaches that the Holy One, Blessed be He, overturned the mountain above the Jews like a tub, and said to them: If you accept the Torah, excellent, and if not, there will be your burial. Rav Aḥa bar Ya’akov said: From here there is a substantial caveat to the obligation to fulfill the Torah. The Jewish people can claim that they were coerced into accepting the Torah, and it is therefore not binding. Rava said: Even so, they again accepted it willingly in the time of Ahasuerus, as it is written: “The Jews ordained, and took upon them, and upon their seed, and upon all such as joined themselves unto them” (Esther 9:27), and he taught: The Jews ordained what they had already taken upon themselves through coercion at Sinai.

Dairy foods - ... a correct reason for this: that when Bnei Yisrael stood at Har Sinai and accepted the Torah and they went down from the mountain to their homes they found nothing to eat immediately except for dairy foods because for meat they would need much preparation to slaughter with a checked knife like Hashem commanded... ... therefore they choose on account of the time to eat dairy foods and we do this as a commemoration of this.

...We have a custom everywhere to eat dairy food on the first day of Shavuot. And it seems to me that the reason is: It is like the two foods that are taken on the evening of Pesach, a reminder of the Korban Pesach and a reminder of the Korban Chagiga, so too we eat a dairy food followed by a meat food, and we bring with them two loaves on the table in place of the Mizbeach, and thus there will be a reminder of the two loaves that were brought on "The day of the Bikkurim."

(11) Let them be ready for the third day; for on the third day the LORD will come down, in the sight of all the people, on Mount Sinai.

Be Ready: Perhaps a person shouldn't sleep on them at night, because they will hear the voice of God in the morning, like the way of the Kohen Gadol on Yom Kippur.

...We have the custom to spread out plants on Shavuot in the synagogue and in houses, as a memory for the happiness of the receiving of the Torah. ...

In remembrance of the joy of receiving the Torah: for there were grasses around Mount Sinai, as it says "The flocks and cattle shall not graze..."