The Midrash writes (Shir Hashirim Rabbah 1:2) that Bnei Yisrael slept the entire night before they received the Torah, as sleep in the Shavuot season is pleasant and the night was short. Not even a mosquito disturbed them. When Hashem came before daybreak to give them the Torah, He found them asleep and had to wake them from their sleep. This is what Hashem asked: "Why is it that I have come and there is no man? [Why is it that] I have called and there is no one who answers?" (Yeshaya 2:2) Therefore, it is the Jewish custom to stay awake all night on Shavuot, to atone for the sin that they were not awake on the night before Matan Torah

Why does the Midrash need to describe the way Am Yisrael slept on the night before they received the Torah, "The sleep in the Shavuot season is pleasant ... Not even a mosquito disturbed them." Why criticize Am Yisrael?

Furthermore, how is it possible that during the most important moment of Matan Torah Am Yisrael goes to sleep? The entire point of Sefirat Ha'omer is to demonstrate Am Yisrael's desire to reach the day upon which they would receive the Torah. Yet, when the fiftieth day arrived, the day they were to receive the Torah – they went to sleep. Is this conceivable? This can be compared to a bride counting the days to her wedding only to go asleep at the time of the chupa. Is this conceivable?

Am Yisrael did not sleep that night because they belittled Matan Torah. Rather, they must have thought that this was the proper way to receive the Torah. The question is why.

The Lubavitcher Rebbe writes in his book, Sha'arei Hamoadim as follows: Am Yisrael thought that their ability to perceive and come close to Hashem while the soul is in the body will never be on the same level as the soul before it descended into the body. The body is material and it cannot contain such a close relationship. However, while the body is asleep, the soul extends out from the body and rises above. Therefore, the soul can receive much greater perceptions when the body is asleep. (Sleep is considered one-sixtieth of death.) Am Yisrael thought that the preparation for receiving the Torah required the soul to extend out from the body in order to achieve great spiritual heights - making undisturbed sleep very important.

This was their big mistake. The Torah has to be received body and soul. The entire nature of Matan Torah is for human beings, who belong to the material world, to elevate their material body through the Torah. This is why Moshe Rabbeinu fought with the angels when they argued: "Place Your majesty on the heavens." (Tehillim 8:2)

[Hashem] told him: Grasp My Throne of glory and give them an answer. [Moshe] said before Him: Creator of the world, the Torah that You are giving me, what does it say? ... "You shall not swear," is there any commerce among you [angels]? ... "You shall not steal, is there any jealousy among you? Is there any evil inclination among you?

Why do you need the Torah? Angels do not need the Torah because they are spiritual. It is the material humans, who possess evil inclination, jealousy and other bad traits, who need the Torah. They need the Torah to guide and sanctify their lives. Therefore, Am Yisrael had to receive the Torah when their bodies were awake. This was their mistake when they went to sleep, and the reason why we stay up all night every year. We need to atone for this mistake.

The Gemara writes: "Everyone admits that Atzeret (Shavuot) requires also lachem (festive meals). What is the reason? It was the day on which the Torah was given." (Pesachim 68b) On all the holidays there is a dispute whether they can be all for Hashem or whether they must have half for you. However, all agree that on Shavuot it has to be "for you", i.e. food and drink. Why? Because it was the day on which the Torah was given to Am Yisrael.

It could have made more sense to argue the opposite. The day the Torah was given to Am Yisrael should be entirely to Hashem! Instead, this itself is the reason. The Torah was given to Am Yisrael because they are not angels. They eat and drink, engage in business, and the Torah was given in order to sanctify all this. Therefore, it has to be "for you." This is the connection between "Chag Hakatzir" – the holiday of the harvest, working the land – and "Chag Hashavuot" – the holiday of Matan Torah, on which the Torah was received. Our job is to connect between the holy and the mundane, elevate the mundane and make it sacred. This is the nature of Shavuot.