Learning Torah on Shabbos-Importance and effectiveness:[1]

The entire purpose of Shabbos: The entire reason for why god gave the Jewish people Shabbos and holidays is in order so they study Torah.[2] Throughout the week every person is busy working and they do not have time to [properly] study Torah Bekevius [i.e. as an occupation and with a full mind]. However, on Shabbos people are free from work and are able to study Torah properly.[3]

Employees and businessmen:[4] Accordingly, workers and businessmen who do not occupy themselves with Torah study constantly throughout every day of the week, should not spend too much time on Shabbos in pleasure of eating and drinking, and it suffices for them to make do with a little bit of pleasure, as they need to study a lot of Torah on Shabbos.

Rabbis, Torah scholars, and Kolel Yungerlight and Yeshiva Bochurim: However, Torah scholars who occupy themselves with the constant study of Torah throughout all of the days of the week should spend some extra time involving themselves in the pleasure of eating and drinking being that they involve themselves in the pleasure of their learning throughout all the days of the week.[5] Nevertheless, they too must occupy themselves with Torah study on Shabbos and are not allowed to spend their entire day in the pleasure of eating and drinking and sleeping, as the verse states “Shabbos for Hashem your God.”[6] [However, some Poskim[7] rule that they should not study Torah with such depth and exertion as they do during the week, and practically, the widespread custom even for Torah scholars is to study lighter subjects on Shabbos. Nonetheless, other Poskim[8] completely negate this assertion and state there is no issue with a Torah scholar learning Torah in great depth even on Shabbos.]

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[1] Admur 290:5

[2] Admur ibid; Yerushalmi Shabbos 15:3; Beis Yosef 288; M”B 290:7; Ben Ish Chaiy Shemos 2 Hakdama

[3] Admur ibid; Tur 290 in name of Midrash; M”B 290:7

[4] Admur ibid; Rama 290:2 “Workers and Baalei Batim who do not study Torah throughout the days of the week are to occupy themselves with more Torah study on Shabbos then Torah scholars who occupy themselves with Torah study throughout all the days of the week”; Beis Yosef 288; Tanchuma; Pesikta Rabasi end of 23

[5] Admur ibid; Rama 290:2 “Torah scholars should spread a little more time in the pleasure of eating and drinking as they had pleasure from their learning throughout all the days of the week”; Beis Yosef 288; Tanchuma; Pesikta Rabasi end of 23

Other opinions: Some Poskim rule the Torah scholars are specially commanded to study Torah on Shabbos. [Machazik Bracha 290:4; Sefer Habatim; Kaf Hachaim 290:15]

[6] Admur ibid;  Nachalas Tzevi 290:1

[7] Siddur Yaavetz Seder Shabbos Kevius Midrash 8 based on Shabbos 119b and Nedarim 37b “A Torah scholars should not trouble himself with in-depth learning of the Talmud on Shabbos as this is also considered desecration of Shabbos……..as the day of Shabbos must be separate from the weekdays in all matters, and hence even the study of Torah must be with pleasure and not be a burden and difficult. This is true and clear.”; See also Chasam Sofer on Torah Vayakehl ; Kesav Sofer O.C. 72

[8] Machazik Bracha 290:6; Minchas Elazar 4:45; Torah Lishma 110; Kaf Hachaim 290:15; See Yabia Omer 2:18; Piskeiy Teshuvos 290:6

[9] Ben Ish Chaiy Shemos 2 Hakdama

[10] Ben Ish Chaiy Shemos 2 Hakdama

[11] Derisha 430:1; Even Ezra Shemos 20:8; Shuta Mekubetzes Beitza 16b; Piskeiy Teshuvos 290:6