The elevation retention celebration
בסכת תשבו שבעת ימים וגו’ למען ידעו דרתיכם כי בסכות הושבתי את-בני-ישראל בהוציאי אותם מארץ מצרים וגו’
You shall dwell in Sukkos for seven days…In order for your generations to know that I placed the Children of Israel in Sukkos when I took them out of Egypt…
During the weeklong Festival of Sukkos, we leave our permanent homes and enter temporary huts. The Torah says the reason for this is so that we shall know that Hashem placed us in Sukkos when He took us out of Egypt. One opinion is that this refers to the Ananei HaKavod, the Clouds of Glory, that Hashem surrounded us with. They were like a protective forcefield, keeping us safe from the elements. It was climate controlled, and even cleaned the garments of the Jewish people. It would seem then that the holiday of Sukkos is to commemorate this miraculous environment that Hashem placed us in. However, one could ask why this miracle in particular merited its own weeklong holiday. As well, the famous question is if this is the purpose of Sukkos, why do we celebrate it in Tishrei, when the Jews left Egypt in Nissan?
We just finished the Ten days of Repentance. We completed the avodah of Yom Kippur. It would not be surprising to find someone becoming laxer in their Divine Service. Once the burden of this time has passed, a person could breathe a sigh of relief and “get back to normal”. However, the goal of this time wasn’t to “get through it”. We were supposed to elevate ourselves in our observance, hopefully becoming more scrupulous.
To instill this proper attitude, Hashem immediately commanded us in the mitzvah of Sukkah. We are to enter a place of complete holiness, surrounded by Hashem’s presence. In such an environment, it’s impossible to become lax and throw off the yoke of Heaven. It is for this same reason that Hashem chose to surround the Jews with the Clouds of Glory. Despite having seen Hashem’s mighty hand in Egypt, there was a concern the inspiration would wear off with time. Therefore, Hashem surrounded them with His presence. It was impossible for the inspiration to wear off, as Hashem was always tangibly with them.
It’s clear then why Sukkos is in Tishrei, and not Nissan. The main focus is to retain the inspiration from the Ten Days of Repentance, similar to the inspiration the Jews felt at the Exodus. Hashem said we have to surround ourselves with this presence, represented by the Sukkah, just like the Jews were surrounded by the Clouds of Glory in the wilderness.
In this vein, we can similarly understand the Festival of Shemini Atzeres, which immediately follows Sukkos. Our Sages tell us that the idea behind the Festival is that once the “party is done” and everyone has left, Hashem requests that we stick around one more day. As His beloved, it’s hard to part so quickly. Another way to look at this idea is it’s an extension of what we said above. Once we achieved such spiritual heights during the days of Rosh Hashanah through Yom Kippur, Hashem wants us to retain that level, at least for one more day. The mitzvah of the day is purely simcha, outside the Sukkah. This way, we can demonstrate that we’ve retained this inspiration, even upon leaving the spiritual incubator that the Sukkah represents.
To this end, we demonstrate our joy through the Torah. We want to show that we are so excited for Hashem’s Torah and His mitzvos, that they’re not a burden for us. They’re not something we’re excited to cast aside once the month of Tishrei ends. The effects of this day of celebration will then surely last us the entire year.
Wishing you a Chag Sameach, a joyous Yom Tov!
 Based on Moadim U’Zmanim 1:85, by Rav Moshe Shternbuch shlita
 Leviticus 23:42,43
 Sukkah 11b
 See Derech Hashem 4:8:2
 Deuteronomy 8:4 with Rashi
 Tur Orach Chaim § 625
 Rav Shternbuch adds that the days between Yom Kippur and Sukkos are simply to prepare for the Festival appropriately
 Sukkah 55b and Rashi to Leviticus 23:36
 See also Teshuvos V’Hanhagos 5:222