We read in Parashat Vayeitzei of Lavan’s agreement with Yaakov, allowing him to marry his daughter, Rachel, after shepherding his flocks for seven years, and how Lavan broke the agreement by bringing his other daughter, Leah, instead of Rachel. After Yaakov protested, Lavan said he would allow Yaakov to marry Rachel, too, the next week, in exchange for an additional seven years of service (29:27).
The Talmud Yerushalmi (Mo’ed Katan 1:7), cited by Tosefot (Mo’ed Katan 8b), points to this verse as the Biblical source of the rule of “ein me’arvin simcha be-simcha,” which forbids combining two festive occasions into a single celebration. According to the Talmud Yerushalmi, Lavan’s insistence that Yaakov first complete the seven-day celebration of his marriage to Leah before marrying Rachel reflects an accepted halakhic principle, requiring that each happy occasion be given its own celebration. And thus, for example, one may not get married on festivals, in order not to combine the joy of the Yom Tov with the joy of the wedding. The Talmud Bavli (Mo’ed Katan 8b) cites a different source for this halakha, noting the account in Sefer Melakhim I (8:65) of the seven-day celebration for the completion of the Beit Ha-mikdash. This celebration was held for seven days before Sukkot, and the Gemara explains that this was done so as not to combine this celebration with the celebration of the festival.
A number of Acharonim addressed the interesting question as to why, in light of this halakha, we are allowed to conduct a festive celebration on Simchat Torah for the completion of the Torah. The festival itself – Shemini Atzeret – already requires a celebration by virtue of its being Yom Tov. Seemingly, then, it should be forbidden to also celebrate the completion of the Torah reading on this day. Interestingly enough, Rav Yitzchak Minkovsky of Karlin, in his Keren Ora commentary to the Talmud (Mo’ed Katan), draws proof from the customary Simchat Torah observance that it is permissible on Yom Tov to conduct a siyum celebration upon the completion of the study of a text. If Halakha permits celebrating the completion of the annual Torah reading cycle on Simchat Torah, Rav Minkovsky writes, then it should likewise be permissible to celebrate, for example, the completion of the study of a Talmudic tractate on Yom Tov. The question remains, however – as Rav Minkovsky himself notes – as to why this is permissible.
Several answers have been suggested to this question (as briefly cited by Rav Asher Anshel Schwartz, Ma’adanei Asher, Parashat Vayeitzei, 5777). The most straightforward, perhaps, is the answer cited in the name of Rav Shlomo Zalman Auerbach, in Halikhot Shelomo – Moadim (chapter 21, note 19). He explained that the rule of “ein me’arvin simcha be-simcha” forbids combining two fundamentally distinct festivities, such as a wedding and Yom Tov, or, in Yaakov’s case, one’s marriages to different women. On Simchat Torah, however, both celebrations – the Yom Tov, and the completion of the Torah reading – involve the same experience of joy, rejoicing over our relationship the Almighty. The celebration of Yom Tov, Rav Shlomo Zalman explained, requires more than simply indulging in fine food and drinks. The obligation is to celebrate our special relationship with God, a relationship which is manifest in our devoted study and observance of the Torah. Celebrating the completion of the annual Torah reading – or, for that matter, any other unit of Torah learning – is thus directly relevant to the celebration of Yom Tov, and in fact enhances our celebration of our closeness to the Almighty. As such, this does not violate the rule of “ein me’arvin simcha be-simcha.”