Torah Study on Shabbat: A Forbidden Activity?
While one should certainly allocate time for Torah study on Shabbat, it is not very well known that one may not engage in intricate or in-depth Torah study on Shabbat. This is especially true regarding Talmud study which is known to be one of the more difficult and strenuous areas of Torah scholarship. Indeed, some authorities argue that in-depth Torah study on Shabbat is considered to be a form of Shabbat desecration through the excessive exertion, mental agony, and toil that is characteristic of such study. Some even suggest that one might be violating the prohibition against "borer" when reflecting on different theories and arguments on Shabbat. One is similarly advised to avoid learning completely new and unfamiliar material on Shabbat.
It is explained that the reason for this quasi-ban on in-depth study on Shabbat is because it detracts from the requirement to spend Shabbat engaged in pleasurable activities (oneg shabbat). Indeed, we are told that Rav Zeira would go around and interrupt those who spent too much time studying on Shabbat, insisting that they engage in more pleasurable pursuits. Furthermore, it is suggested that one who generally studies Torah in-depth during the week might be violating the prohibition against engaging in weekday activities (uvdin d'chol) by doing so on Shabbat! According to this approach, one should preferably study Midrash, Aggada, or Mussar on Shabbat. According to the Rebbes of Chabad, on Shabbat one should spend two-thirds of one's study time focused on nistar, also known as Chassidut, and one-third of one’s study time focused on nigleh, all the other routine subjects. The Chafetz Chaim is said to have studied chumash with commentaries on Shabbat.
The ban against strenuous and intensive learning on Shabbat is often observed in varying degrees, all in accordance with a person’s personal study needs and goals. Some suggest that the source for this practice is based on the Meiri, who writes that a Torah scholar should focus on sleep, rather than study, on Shabbat. Some authorities even suggest that one who feels that intensive Torah study is pleasurable should, nevertheless, avoid it on Shabbat. This is because it is argued that it is inevitable that during the course of such study one will encounter at least some intellectual frustrations which could detract from one's Shabbat experience.
Of course, the halacha is not in accordance with any of the views cited above, and one is permitted to engage in any type of Torah study on Shabbat that one desires. This includes even the most intensive and strenuous areas of study, should one enjoy them. Regardless of what one studies on Shabbat, one should try to come up with new Torah insights. This is because we are taught that when one's additional soul (neshama yeteira) departs at the conclusion of Shabbat and returns to its Heavenly repository, it is asked to present any new Torah insights or thoughts that one had over the course of Shabbat. It is even written that Shabbat was given specifically for engaging in Torah study.
 Tur, OC 290; OC 290:2.
 Siddur Yaavetz, Beit Hayayin 8. See Yabia Omer 2:18 for an in-depth treatment of this issue.
 Nedarim 37b.
 Rav Yaakov Emden, Gittin 60a; Derech Chaim (Maharal), Introduction to Pirkei Avot.
 Rashi, Shabbat 119b.
 Minhag Yisrael Torah, OC 290:2.
 Temura 14b.
 Iggeret Hagra.
 Kol Kitvei Hachafetz Chaim Hashalem p.31.
 Tzipichat B'dvash 23; Meiri, Shabbat 118a.
 Petach Hadvir 290:5.
 Torah Lishma 111; Minchat Elazar 4:45.
 Machzik Beracha 290:6; Minchat Elazar 4:45.
 Shaarei Teshuva, OC 290.
 Yerushalmi Shabbat 15:3.