The obligation to serve God in joy is rooted in the Torah itself: Devarim 28:47 frames the great curses as the consequence of failing to serve God "in joy and gladness over the abundance of everything," implying that joyful service is not merely praiseworthy but required.
The Gemara in Shabbat 30b draws the sharpest distinction: the Divine Presence rests upon a person only from an atmosphere imbued with the joy of a mitzva — not from sadness, laziness, laughter, or idle talk — and Rav Yehuda explicitly extends this principle to matters of halacha, meaning that Torah study itself must be conducted in that same spirit of mitzva-joy.
Tanna DeBei Eliyahu makes the joy of Torah learning a theme in two passages: Tanna DeBei Eliyahu Rabbah 4 declares praiseworthy the person who delights himself in words of Torah like an animal plowing a field, and credits such a person with bringing light and blessing into the world; and Tanna DeBei Eliyahu Rabbah 25 teaches that when Israel engages in Torah, God Himself rejoices in them, and that renewed Torah study in the synagogue and study hall brings fresh joy before God each and every day.
אור החיים, דברים ז יב teaches explicitly that Torah must be studied in joy and not in sadness, reading the word "ekev" as pointing to joy as the very reward of Torah engagement — and connecting this to the Mishnah's teaching that one mitzva draws another, with joy itself being the reward of mitzva.
Mishneh Torah, Shofar, Sukkah and Lulav 8:15 codifies this as a principle: the joy a person feels in performing a mitzva and in the love of God who commanded it is itself a great form of divine service.
Mesillat Yesharim 19 calls joy an essential and foundational pillar of serving God, citing David's call to "serve God with joy" (Tehillim 100:2) and the rabbinic teaching from Shabbat 30b that the Divine Presence rests only through joy of a mitzva; and Mesillat Yesharim 7 adds that outward alacrity in performing a mitzva kindles inner spiritual fire, while sluggishness extinguishes it.
Duties of the Heart, Third Treatise on Service of God 10 locates joy among the soul's proper dispositions, specifying that diligence belongs precisely to spiritual pleasures and deeds aimed at attaining the favor of God.
Sdei Chemed, Maarechet Alef 314 cites the principle that a person learns Torah only in the place where his heart desires — underscoring that heartfelt desire and inner engagement are the preconditions of genuine Torah study.
מכתב מאליהו, חלק א עמוד קג grounds this further, teaching that true understanding of Torah comes only from deep longing and desire — for comprehension follows the intensity of one's passion — and that only through such desire does one's Torah truly become one's own, to contemplate day and night.
Tanya, Part I; Likkutei Amarim 31 rules explicitly, citing the Arizal, that worry over sins is appropriate only during confession and not during prayer or Torah study, which must be conducted with joy drawn from the side of holiness — and that this joyful service, the soul rejoicing as it returns to its Father's house, is to be one's lifelong work; while Tanya, Part I; Likkutei Amarim 26 adds that just as a wrestler who is sluggish will be thrown even if stronger, so too the evil inclination cannot be conquered except through the alacrity born of joy and a heart free of worry and sadness.
Likutei Moharan, Part II 24 calls it a great mitzva to always be in a state of joy and to forcefully distance gloom and depression, recognizing that human nature pulls toward sadness through life's hardships — and therefore one must exert great effort to bring oneself to joy by any means possible; while Likutei Moharan 24 adds that the primary elevation of holiness is achieved through joy.
Levush, Orach Chayim 47:1 reads the brachah over Torah through this lens, explaining that one must show that Torah is precious and a source of delight — using language of joy and promenade — just as one makes a brachah over all of life's pleasures.
Ein Aya, Berakhot 6:37 distinguishes two modes of loving Torah — love for its intrinsic sacred worth versus the general human love of knowledge — and insists that Torah's love must be for its own holy sake, so that even material already learned appears each day as fresh, and from that quality of love one is enabled to receive new insight as well, like an ever-strengthening spring.
Rashi on Kohelet 5:17 reads the verse's call to "eat and drink and see good" as an invitation to engage in Torah — the good doctrine — and to rejoice in one's portion rather than chasing wealth, linking simcha with the very act of Torah engagement.
Kiddushin 30 captures the dynamic interior to Torah study itself: even a father and son or teacher and student may become antagonists in the intensity of their learning, yet they do not leave until they have become beloved to one another — the word "vahev" being read as love — showing that the fire of Torah debate resolves into deeper connection and joy.