One of the main characteristics of Shavuot is the custom for men to stay awake all night to learn Torah. The Magen Avraham explains the reason for this Minhag (custom). Our Sages state that Bnei Yisrael overslept the night before the Torah was given and Hashem had to wake them up to receive it.
It is the reason we stay awake on Shavuot, to rectify the mistake made by our ancestors. The Arizal guarantees that one who stays up to study Torah the whole night of Shavuot will merit a peaceful year and know no harm.

But how do we understand that a generation as holy as they were, fell asleep at such a crucial moment? We know that they longed to receive the Torah since they agreed to accept the laws even before they even knew them! So why did they show so little enthusiasm the night before Matan Torah?

We also need to understand how staying awake rectifies their mistake.

Some commentators explain that Bnei Yisrael deliberately went to sleep that night; they thought that by doing so, they would be able to create a special bond with Hashem in their sleep.

The rule is that whenever important personalities stumble and commit a "fault", they always presented valid reasons to do so. However, their actual transgression shows that the Yetzer Hara had led them to err. But what was the underlying motivation that drove them to sleep on that significant night?

The Jewish people sincerely wanted to receive the Torah, as their statement "Naasseh Venishma" (we will do then we understand) demonstrates. However, they still felt some discomfort, a subtle uncertainty. They realized that accepting the Torah implied a number of obligations and responsibilities. The life of a practicing Jew is certainly one that provides the most satisfaction, but that also requires much effort and work on oneself. Therefore, an individual may be tempted to "escape" these challenges in a variety of ways, including through sleep.

People who are suffering or going through difficult times tend to want more sleep than necessary. It is a way of showing their will to escape their ordeal.

The Jewish people might have been apprehensive of the new responsibilities incumbent upon them. So the Bnei Yisrael unconsciously tried to "escape" the "discouraging" elements of Matan Torah. This escape was in their case, sleep.

The minhag to stay awake all night to study Torah comes to "rectify" this subtle fault. This proves that we, on the other hand, are willing to face the responsibilities that accompany the observance of the Torah. We realize that although this task is not easy, respect for the Torah is the most rewarding path. Avoiding challenges does not guarantee real satisfaction, it is only by confronting them that one can really feel fulfilled.

Rabbi Noach Weinberg zatzal often told his students that nothing can be learned without difficulty. Each important experience inevitably involves great effort as well as personal sacrifices.

This is particularly true when studying and following the Torah and its ways; some of the greatest geniuses have failed in their study of Torah, unwilling to make the considerable efforts needed to understand its depth. Only those who were ready to invest the extra effort and pushed themselves to grow found out the real pleasure that is the studying of Torah and ultimately rose to high levels.

Some people oppose the custom of staying awake all night studying Torah. They think that one will end up studying less while staying awake all night than keeping his habitual sleeping rhythm. Statistically, this argument seems logical and correct. Those who do not sleep Shavuot night usually rest for a few hours the day before Yom Tov, then recuperate after Shacharit (the Morning Prayer) and often will rest a little after lunch!

However, Rav Yitzchak Berkovitz shlita underlines the error of this reasoning; if the purpose of the evening was to study as much as possible, this evidence would have been justified; it would have been better to sleep as usual during the night and then study during the day. But that's not the purpose. As we have seen, it has the purpose of preparing us to face the challenges that the Torah presents. In sacrificing one’s night's sleep, we show that we do not want to "escape", but rather recognize that the only way to live a meaningful life is to face its difficulties and overcome them.

May we all merit to receive the Torah with joy, eagerness, and subservience.