1. Parallels Between Sukkos and Pesach
We know there is a mitzvah to build a sukkah—temporary dwelling—and to sit in the sukkah during the festival of Sukkos. There are notable similarities between the festival of Pesach and the festival of Sukkos. Both are among the three pilgrimage festivals, when Jews would ascend to the Beis HaMikdash three times a year: Pesach, Shavuos, and Sukkos. Shavuos is only one day, while both Pesach and Sukkos last seven days, though Sukkos has an additional eighth day, Shemini Atzeres.2. The Obligation to Eat on the First Night
A key similarity between Pesach and Sukkos is that on Pesach we are obligated to eat matzah—unleavened bread—on the first night. On Sukkos, there is a mitzvah to eat in the sukkah. However, there is no obligation to eat specifically at night except for this first night. The Torah teaches that on the first night of both festivals, there is a unique requirement: just as one must eat matzah on the first night of Pesach, so too must one eat in the sukkah on the first night of Sukkos.3. Minimum Quantity for Fulfilling Eating Mitzvos
Halacha specifies a minimum amount that must be eaten to fulfill these mitzvos: a kezayis—an olive’s bulk. For example, the Gemara tells a story about Rebbe who was very ill but still ate more than a kezayis in order to fulfill his obligation on Sukkos. Eating less than this amount does not constitute fulfilling the mitzvah; it is considered merely snacking (achilas arai). Only eating at least a kezayis, which is considered significant eating (achilas keva), fulfills the mitzvah.4. When Is Eating in the Sukkah Required?
On Sukkos, if someone wants to eat bread or other foods requiring a meal, they must do so in the sukkah. However, if one does not wish to eat or only eats foods that do not require sitting in a sukkah, such as snacks or small quantities less than a kezayis, there is no obligation to use the sukkah. This applies throughout most of Sukkos except for the first night.5. The Special Obligation of Leil Rishon Shel Sukkos
The Torah teaches us through a gezeirah shavah—a verbal analogy—that just as there is an obligation to eat matzah on the first night of Pesach, so too there is an obligation to eat in the sukkah on the first night of Sukkos. Even if one would prefer not to eat or would normally avoid eating in certain circumstances (such as when it rains), on this first night one must nevertheless fulfill this mitzvah by eating at least a kezayis in the sukkah. After this first night, one may choose whether or not to eat in the sukkah, depending on their needs.6. Why Is This Special Teaching Necessary?
One might ask why we need this special teaching from the Torah requiring eating in the sukkah on the first night—isn’t it logical? After all, on Yom Tov there is an obligation to have a festive meal (seudah). To fulfill this mitzvah properly, one would need to eat bread or another significant food item, which already requires sitting in a sukkah. So why does Torah need to specify this requirement? The answer given by some authorities is that technically, one could fulfill their Yom Tov meal with other foods that do not require sitting in a sukkah, such as fruits or light snacks. Therefore, without this special teaching, it would be possible for someone never to enter their sukkah. The Torah thus makes clear that on this first night there is an absolute obligation.7. The Case of Rain and Other Exemptions on Leil Rishon Shel Sukkos
Normally, if it rains during Sukkos and conditions are uncomfortable (mitzta’er—suffering), one may leave the sukkah. However, regarding this special obligation of eating in the sukkah on leil rishon (the first night), some authorities maintain that even if it rains or conditions are unpleasant, one should still strive to fulfill this mitzvah by eating at least a minimal amount in the sukkah. Others hold that even here exemptions apply and that discomfort can exempt you from sitting in the sukkah, but ideally one should try their utmost.8. Timing and Customs Relating to Eating in the Sukkah at Night
There are also discussions regarding when exactly one should perform this mitzvah at night—whether before or after dark—and how closely it should resemble how we perform similar mitzvos on Pesach with regard to timing and manner. Some communities have customs based on these parallels: just as we wait until after dark for eating matzah at Pesach’s seder night, so too some wait until after dark before eating bread in their sukkahs on leil rishon shel sukkos. Others may begin earlier according to their tradition but strive for similarity between these two festivals’ practices wherever possible.