"You shall dwell in booths for a seven day period, every native in Israel shall dwell in booths so that your generations will know that I caused the Children of Israel to dwell in booths when I took them from the land of Egypt; I am Hashem, your G-d"(Vayikra 23:42-43). Rashi, citing from the Gemarah Sukkah (11B) understands the above in accordance with the teaching of Rabbi Eliezer, that Sukkahs are the annual commemoration of the ananei hakavod- Clouds of Glory in which Hashem enveloped the Jewish nation during their forty year trek in the desert. The "climate control" setting of these clouds provided air conditioning during the day and heat at night. It is no wonder we celebrate Hashem's Divine providence and protection. Yet one has to ask, given that the three shepherds that led the Jewish nation, Moshe, Aharon and Miriam, each contributed a major phenomenon - Moshe the mon, Miriam the be'er and Aharon the ananei hakavod - why do we have a yom tov to commemorate Aharon's gift while the other two are seemingly neglected?
An answer to the above may be culled from the commentary of the Gra (Vilna Gaon) on the opening verses of Shir HaShirim, and his commentary Aderes Eliyahu on Shmos (34:10). The Tur (Orach Chaim 625) writes that Sukkos is observed at the time when people are returning to their homes after the Summer to clearly indicate that our exiting our homes is for the sake of the mitzvah as opposed to our personal comfort. The Gaon provides another reason why Sukkos is celebrated in the Fall and not in the Spring when we left Egypt. The Gra opines that since the yom tov of Sukkos is to remember Hashem's protective clouds, the Jewish nation were first introduced to the clouds immediately after the exodus, as the Torah (Shmos 13:21) informs us: "Hashem went before them by day in a pillar of cloud to lead them on the way". Why then do we not celebrate Sukkos in the Spring? We should conduct the Pesach Seder in the Sukkah.
The Gra answers that when Bnei Yisroel committed the sin of the golden calf (on the 17th of Tammuz) Hashem withdrew the clouds and His apparent benevolent protection from the people. It was only after Hashem pronounced "Solachti kidvorecha" (Bamidbar 14:20) on Yom Kippur, and after the people responded enthusiastically and generously with their wealth and willingness to the commandment to construct the Mishkan, that the clouds return.
What happened subsequently is most remarkable. The clouds did not only return, but they were of much greater magnitude. Whereas prior to the sin of the golden calf the clouds enveloped only the righteous members of the nation, they now provided TLC to all. This is how the Gra understands the verses immediately following the Thirteen Attributes of Hashem, and His forgiveness of the Jewish people for the sin of the golden calf. Hashem said: "Behold! I seal a covenant before your entire people I shall make distinctions (wonders) such as have never been created in the entire world and among the nations, and the entire people among whom you are will see the work of Hashem- which is awesome- that I am about to do with you." (Shemos 34:10)
The wonders that the verse is referring to are the clouds that returned enveloping the entire nation. It is for this reason that Sukkos is celebrated in the Fall, as we are reliving the experience of the second set of Ananei HaKavod that appeared in the Fall, following Yom Kippur, not the first set that arrived in the Spring.
A most exciting phenomenon emerges: The Jewish nation backslid and sinned: they commit the grave sin of the golden calf, and then Moshe leads the nation in Teshuvah. Had Hashem restored the relationship to its prior state before their sin, that would have been dayeinu - sufficient. We would have celebrated the return of the Shechinah, Divine Presence. What happened was the extraordinary! The relationship between Hashem and the people was not only restored, but improved and enhanced.
The fact that Sukkos follows Yom Kippur is not accidental, nor coincidental, but is rather the actualization of one of the basic tenets of Yom Kippur. The latter not only has the capacity to atone, but as Reish Lakish teaches (Yuma 86B): Teshuvah that is performed b'ahavah, motivated by love of Hashem, has the ability to transform willful transgressions into merits! Thus Sukkos serves as an annual symbol and testimony of not only our renewed relationship with Hashem, but our improved one.
It is thus understandable why Sukkos enjoys the distinction of being the happiest Chag. Its very reference and identification in the prayers is Zman Simchaseinu. Moreover, every morning in the bracha prior to Shema, we proclaim "Ahava rabbah ahavtanu - with abundant love Hashem has loved us". The proof of that love is the next verse - "chemlah gedolah v'yesara chamalta oleinu - with exceedingly great pity have You pitied us". The Gra explains that this line refers to the great reversal that took place after the Golden Calf. Initially, Hashem says to Moshe, "I will destroy them and make a nation from you." After Moshe's prayers and the nation's Teshuvah, Hashem not only forgives, but extends His Divine Presence that was at Sinai for a brief period to dwell permanently in their midst in the Mishkan. Not a return of Shechinah, but an upgrade.
Finally, it is understandable why we have a holiday to celebrate Aharon's contribution of the Clouds more than Miriam's well and Moshe's mon. The latter two were necessities. Hashem brought them into a desert, and thus He had to provide them with the basics of nourishment. But an improved all-weather comfort system for the entire nation that showed a special love and affection, that we excitedly reciprocate and return on Sukkos.