The Zohar (vol.1, 8:) mentions the minhag to study Torah all night long on Shavuos: "Reb Shimon and his holy students were singing the Torah and creating chiddushim [Shavuos night]... and they were very joyous. Reb Shimon told them, 'My children, you are fortunate because tomorrow the kallah [the Torah] will go to the chuppah with you – and only with you – because you are making the tikun tonight, and you are rejoicing with the Torah... Hakadosh Baruch Hu will bless you with seventy brachos and put a crown on your head... Whoever joins us on this night will be protected... the entire year. He will live the year in peace.'"
The Magen Avraham (494) writes, "The Zohar (vol.3, 98.) tells us that the early chassidim would remain awake the entire night of Shavuos and study Torah. This is the current custom today for most Torah scholars. We can explain according to pshat: Bnei Yisrael slept all night [before matan Torah], and Hakodosh Baruch Hu had to wake them [to receive the Torah], as the Midrash tells us. Therefore, we must rectify this."
The Shlah HaKadosh (Masechta Shavuos, Ner Mitzvah, 8) quotes the following episode, as it was told by Reb Shlomo Alkabetz (who composed the Lecha Dodi) zt'l: "[Shavuos night], we were studying Mishnayos. We completed two masechtos, and then Hashem granted us to hear a bas kol from Heaven that said, 'My beloved, righteous friends, peace to you. You are so fortunate. Ashreichem! You are fortunate, and your parents who gave birth to you are fortunate. You are fortunate in this world and the next world, for you devoted yourself to crown Me on this night. My crown has fallen years ago, and no one has consoled me since then. I was thrown to the earth; I lie in rubbish. You returned the crown to its place! Be strong, My friends, whom I love. Be happy! Rejoice! You are exalted people... Your kol Torah rises before Hakadosh Baruch Hu and breaks through several heavens. The malachim... are silent. Hakadosh Baruch Hu and all the hosts of heaven listen to your voices... You earned this greatness. You are fortunate, and so are your parents who gave birth to you... because you didn't sleep this night and because I was elevated this night. Therefore, be strong, be happy, My children, My beloved. Rejoice... and don't stop your studies... Your Torah study is sweet before Hakadosh Baruch Hu. Stand on your feet and elevate Me and say in a loud voice like on Yom Kippur, ועד לעולם מלכותו כבוד שם ברוך'... and they did so."
The Seder HaYom (Shavuos) writes, "On the night of Shavuos, one should remain awake and study Torah all night long, (or, at least, you should study Torah most of the night) ... Don't take this matter lightly because a person might be low and unimportant in one area and have amazing strengths in other ways. He sustains the entire world – and that is something that even the malachim can't do. He gives strength to Hashem, the Creator of the world... And, chas veshalom, [if one sins], he weakens the strength of Heaven and draws His right hand back. As it states, תשי ילדך צור, 'You weakened the strength of the One Who created you.' "Therefore, every person, והדיוט שבקטנים קטן שבהדיוטות, even the lowest and most simple person, should consider himself great and say, 'Perhaps I can fulfill Hashem's will.' ... Don't say, 'Who am I, and what is my worth that the worlds should be rectified through me?' ... Such thoughts cause disaster – onto oneself and others – because [if he thinks so], he won't be cautious with his deeds..."
These words contain an essential lesson, not solely regarding the night of Shavuos. We shouldn't underestimate our potential. Great things can happen through us. Even if we are simple, regular people in many ways, this doesn't mean we can't have moments of greatness. And on the night of Shavuos, when regular people like us stay awake and study Torah, we create great tikunim. Many blessings and salvations, b'ruchniyus and b'gashmiyus, come from this to us and all Yidden.
Some people have פסולה ענוה, the wrong type of humility. They think the tikkun that happens on this night is reserved only for great tzaddikim. But we have to recognize our potential.
We continue with the Seder Hayom's lesson: "If he feels exhausted and has to sleep, he can sleep, but not [in a bed], so he won't sleep too long. And then he should quickly awaken and study Torah until daybreak. And then he should praise Hashem in the beis medresh [at Shacharis] for all the kindness Hashem performs for us. He gave us His Torah and chose us from all nations to be His beloved nation. How fortunate is our lot!"
Reb Shalom Ber of Lubavitch zt'l writes that he has a note, handwritten by his grandfather, the Tzemach Tzedek zt'l, with the following notation: "I guarantee that whoever stays awake all Shavuos night and studies Torah will merit the crown of Torah." Rebbe Shalom Ber zt'l added, "The Tzemach Tzedek was a posek and a Rav, so the way he rules in this world is how the beis din rules in heaven. Therefore, one must be awake the entire night and toil in Torah. The main thing is בלילה נעור, (with an emphasis on the word נעור) to be awake [and not when one studies with laziness]."
Every Shavuos morning, after davening Shacharis with the neitz hachamah, Reb Chaim Leib Aurbach zt’l (the father of Reb Shlomo Zalman Aurbach zt’l) would go to Reb Moshe Yosef Hoffman zt'l, the Pupa dayan of Yerushalayim, to wish him "a gut Yom Tov."
One year, Reb Chaim Leib asked the Pupa dayan, "I see that you are extremely happy today. Why is that?" The dayan replied, "I wasn't planning to tell you, but since you asked, I will tell you. The Chasam Sofer zt'l said that whoever studies the entire night of Shavuos without interruption (without הדעת היסח) will merit giluy Eliyahu, seeing Eliyahu HaNavi. When I was a yeshiva student, I studied in the Ksav Sofer's yeshiva in Pressburg and on Shavuos, the yeshiva students always strived to study Torah without interruption Shavuos night to merit giluy Eliyahu. I also tried for many years, but I never merited giluy Eliyahu. Last night, I was learning a difficult passage in the Zohar; I couldn't decipher its holy words. Then, an elderly person, whom I'd never seen before, came into the beis medresh. He explained the Zohar to me in a beautiful way. I closed my eyes to figure out whether his explanation answered all my difficulties. When I opened my eyes, the man wasn't there anymore, and it was time to daven Shacharis. Now you understand why I’m so happy this morning."
Someone asked Reb Shlomo Zalman Auerbach zt'l whether he should remain awake all night on Shavuos. He explained that he knows that he will learn much more Torah over Shavuos if he has a regular night's sleep. Reb Shlomo Zalman replied that although he had a valid point, he should nevertheless study Torah all night. Reb Shlomo Zalman explained, "This is a great principle: One must keep the customs accepted by all Yidden and talmidei chachamim, and he should educate his family to respect customs. Lomdim worldwide keep this custom; if you don't, your children and wife will think you are acting incorrectly. Therefore, I advise you to keep the minhag, even if it is hard" (Halichos Shlomo 12, note 13).
