All the seasonal Mitzvot that commemorate the Exodus are performed on Pesach (Matzvah, Korban Pesach, the retelling of the Exodus story and almost everything done at the Pesach Sedar). Sukkah is the only exception for it is unmistakably designed to recall the Exodus from Egypt (Vaykira 23:42-43) and performed on Sukkot. What is different about the Mitzvah of Sukkah that causes it is to be performed at a different time and a different holiday than all other Exodus Mitzvot.
When looking for a fundamental answer to this question (as opposed to the Tur OC 625 who offers a technical answer explaining that Pesach time is too hot and sitting in a Sukkah for the Mitzvah then would be indistinguishable from others who also are sitting outside enjoying the weather), one would have to investigate the reason why we sit in a Sukkah in the first place. In other words, to understand why we sit in a Sukkah on Sukkot (opposed to Pesach), one would have to ask why we sit in a Sukkah, at all. Only once we uncover why we sit in a Sukkah, can we understand why it’s most appropriate to do that at Pesach time.
In truth, there are two possible reasons offered as to why we sit in a Sukkah (Gemara Sukkah 11b); either to remember the Clouds of Glory, in which Hashem protected us with in the desert, or to commemorate the actual booths that the Jews sat in upon leaving Egypt.
Assuming the Sukkah was designed to commemorate the Clouds of Glory, we sit in the Sukkah on Sukkot because that is the date when Hashem returned the Clouds of Glory to the Jews. Hashem had removed it after the sin of the Golden Calf and returned it the first day of Sukkot (Gr”a quoted by the Siddur Otzer HaTefillot).
Before addressing this question according to the second reason, that we are commemorating the booths that the Jews once sat in, let us pose one more powerful question. Why do we remember such a non miraculous and an uneventful act, such as Jews after the Exodus sitting in a booth? Usually, we remember miraculous events. There were numerous mundane events throughout history; why choose the booths that the Jews sat in to celebrate?
On a simple and historical level, one can respond as the Ibn Ezra (Vayikra 23:42) does by explaining that in the summer it was hot and there was no real need to for anyone to build a Sukkah until the fall, or Sukkot time, when it got cold. However, there is another answer derived from the Rashbam which offers a greater insight into the holiday of Sukkot
The Rashbam (Vayikra 23:43), assuming a Sukkah commemorates the actual booths, explains that the holiday of Sukkot occurs during the harvest season, a time period where a farmer might naturally struggle with overconfidence. After all, it is natural for a farmer (or anyone) to bask in their success. Obligating him (along with everyone else) in the Mitzvah of Sukkah reminds the farmer (along with everyone else) that he is not the real Baal HaBayit (literally owner of the house), and not ultimately the one in charge. True, the farmer’s success was based on his talent, experience, and hard work but success came to fruition only with the assistance of Hashem (see Devorim 8:17-18).
What better way to remind the farmer of Hashem’s involvement than by relocating him into a Sukkah, a temporary dwelling place in which one more easily realizes the instabilities in this world and how Hashem is needed for support. A Sukkah’s roof, symbolizing protection, is made of Schach (crops, wood and greenery). Those crops that were once harvested by the farmer encapsulating the farmer’s hard work and success, are used as a roof. Ultimately this represents Hashem’s protection which is only accomplished via the crops, the farmer’s hard work.
Perhaps this also explains the unusual language the Torah uses to command the Mitzvah of Sukkah. The Torah obligates “All citizens (Ezrach)” (Vayikra 23:42) in the Mitzvah of Sukkah. The language of citizen implies a certain desire the person naturally has for permanence. The Torah directs it language precisely to the desire to go inside a permanent house and risk developing a sense of arrogance due to a successful crop. The Torah responds by commanding us to go out into a Sukkah to remember that Hashem runs the world (See the Kli Yakir 23:42). The Torah instructs us to leave permanent houses and reside in temporary Sukkahs.
Although the Rashbam’s answer successfully explains the Sukkah’s placement on the calendar (Sukkot not Pesach), there is one issue that remains unanswered. How is Sukkah connected to the Exodus? After all, the Pasuk linked Sukkah to the Exodus “In Sukkahs you should sit… so the (future) generations will know that l placed the Jews in Sukkot as I took them from Egypt”? In other words, the Rashbam clarifies why we sit in a Sukkah at Sukkot time, but in doing so seems to completely disconnect Sukkah from the Exodus.
Although classically, the Mitzvot of Pesach are designed to conjure up memories of Hashem miraculously redeeming the Jews from Egypt, there may be another religious value communicated. In contrast to Pesach which celebrates redeeming us from Egypt in such haste, with the 10 plagues, or by splitting the sea, Sukkot marks how Hashem continued to oversee us afterwards. In contrast to Pesach, where we remember or maybe even relive (Rambam Chomatzy U-Matzah 7:6) the actual miraculous departure from Egypt, Sukkot celebrates the post-Exodus experience. Not only did Hashem take us from Egypt in an overtly miraculous manner, he continued caring for on a daily basis in the desert, and Sukkot commemorates just that.
The mundane and unexciting daily care Hashem invested and invests is captured by the Sukkah. Even after preforming the greatest miracles in world history (Ramban in Shemot 13:16), Hashem does not want his non-miraculous care and protection to go unnoticed or unappreciated.
The Chumash’s presentation of the Mitzvah captures precisely this point, as the Pasuk testifies, “In Sukkahs you should sit… so the (future) generations will know that l placed the Jews in Sukkahs as I took them from Egypt, I am Hashem your G-d”. The reason we sit is because Hashem reminds us that even after he took us out of Egypt, he continued caring for us in a normal and non-miraculous manner. Commemorating the actual booths that the Jews once sat in captures Hashem’s help in the mundane. It is precisely the uneventful, mundane booths that we remember and celebrate. Because recognizing Hashem’s hidden hand is so important and easy to overlook, the Mitzvah of Sukkah is designed to assist us in that religious pursuit.
Lastly, the Pasuk concludes with “And I am Hashem your G-d” as if to say, that is part of what a G-d does, cares for His nation in an covert fashion (Netziv Vayikra 23:43). But by not just saying “I am Hashem” and by adding “your G-d” there is a second implication. Its is our responsibility to interact with Hashem as a G-d, in this case search and find him in the mundane.
After all, (besides the Exodus) Hashem never promised us that he would miraculously reveal Himself to us, but that if we look he would allow us to find him.
