Partly from the Sephardic Scoop article written by Rabbi Asher Margaliot a"h
The Magen Abraham, based on a Midrashic account, states: "At the Revelation at Sinai, when the time came for the Torah to be given, many fell asleep and the A-lmighty had to awaken them. We must rectify this through our staying awake and studying Torah through the night" (Orah Hayim 494). How many times during the year have we slept or idled away time during which we should have been studying Torah! How many times were we inattentive while listening to the Torah being read! Indeed, it is appropriate to express our regret at these shortcomings before commemorating receiving the Torah. The Hok Yaaqob, based on the Zohar, explains that the pious remain awake and labor in Torah all night as an expression of eagerness and anticipation for a great, precious event. "Let us go to our possession, the sacred inheritance designated for us and our children". The Zohar commends those who thus quot;anticipate the hour of receiving the Torah, when the people of Israel became joined to the Torah and both became as one." Rabbi Israel Nagara elaborates thus: "since the hour of the giving of the Torah is, as it were, the hour of wedding between Israel and the Torah, it is proper to be engaged in preparing the ornaments of the bride the previous night".
The Rambam, in codifying our ancient traditions regarding the approach to the study of Torah all year long, states: "A person learns most of his wisdom by night." Perhaps the later rabbis chose to establish the main learning of Shabuot at night to also reflect this concept.
The Shelah Hakadosh relates that on Leil Shabuot the Divine Presence was revealed to Maran Rabbi Yosef Karo and his companions, who were studying Torah all that night, and said to them: "Happy are you and happy is your portion." Those who dedicate their speech, actions and thought to Torah study on this night more readily merit the revelation of the Torah's intricacies and achieve a deeper understanding in their learning.
The Kabbalah sages prescribed an order of study. or tikkun, for Leil Shabuot, comprising passages from each Parasha and each Book of the written Torah, plus selections from Mishnah and Zohar. The Ten Commandments are read twice. Megilat Ruth is entirely read as it relates the inspiring story of a on-Jewess fully turning to Judaism.
Some communities read a brief synopsis of the 613 mitsvot. Some communities, in accordance with the Midrashic statement that the Torah was very difficult to understand until Mishle was written, read the entire Book of Mishle, for its parables contain the key to much of the Torah.
Regarding those not initiated into the Kabbalah reading the Zohar portions of the tikkun, or any other portions of Zohar, there are two opinions. Some say reading Zohar is "good for the soul" even if one doesn't understand what he is reading. Others claim that it is more appropriate to skip the Zohar and study those portions of the Torah which one may understand.
The Hok Yaakob is of the opinion that the tikkun was established for the unlearned, but a scholar quot;may study whatever Torah subject his heart desires". In many great Ashkenazic yeshivot the custom of staying up all night was observed but the order of study was Talmud, not the tikkun. Today many scholars do follow the practice of reading the tikkun on this night.
The Ben Ish Hai writes that even if one cannot stay up all night for whatever reason, he should nonetheless recite the Tanakh portion of the tikkun.
May we all continue to go from strength to strength and merit rewards for our study and contemplation of Torah especially on this Festival of the Giving of the Torah.