Tur (O.C. 625) raises a famous question concerning the commandment to celebrate the festival of Sukkos in the Jewish month of Tishrei. If, as the Torah indicates (Emor 24:43), the mitzva of dwelling in a sukka reminds us of the fact that Hashem -- both miraculously through Clouds of Glory (the position of R. Eliezer, Sukka 11b) and through natural means via man-made actual huts in a previously uninhabited desert (R. Akiva, ibid.) -- protected us in the Midbar, the festival should take place in Nissan, the month of the Exodus when Bnei Yisrael first entered the Midbar and received this protection.
Ibn Ezra (ibid.) answers that the Bnei Yisrael only found it necessary to construct actual huts or sukkot from Tishrei onward to protect themselves from the cold. The Ananei HaKavod provided shelter from the sun during the summer months.
Tur himself suggests that Hashem delayed the celebration from the spring to the fall so that our dwelling in the sukkot should be noticeable as a mitzva performance in the not always pleasant fall weather and not be interpreted as a relaxing stay outdoors in the balmy spring weather unrelated to Divine service.
The Vilna Gaon offers an alternative explanation. Since the sukkot commemorate the Ananei Hakavod, we celebrate the date that they remained with us throughout our stay in the desert. After the Cheit HaEigel, the Clouds of Glory left as a punishment for this grave sin. Only after Klal Yisrael started work on the construction the Mishkan which served as an atonement for this sin, did the clouds return. This occurred on the fifteenth of Tishrei, exactly the date of Sukkot, soon after Yom Kippur when Moshe descended with the second Luchot and informed the Jews of the commandment to build the Mishkan.
Bina La'Ittim (quoted in Tal'lei Orot) by R. Azaria Figo offers a novel explanation. Hashem's involvement in the world manifests itself in two ways: first, through the natural order, the fixed rules of creation; second, through, divine providence overriding the regular rules of nature. The goal of creation was that mankind, through their connecting to G-d by fulfilling His Will, would merit the second, transcendent level of Divine intervention in the world. This was to be realized through B'nei Yisrael who committed to fulfilling Hashem's mission for the world as embodied in His Torah. Malbim (B'raishis) explains the concept of the Avot being the "Divine Chariot" as meaning that they were the ones who caused this second, more intense level of Divine intervention to occur in the world, hence fulfilling the Goal of Creation. The ancient Egyptians were steeped in the belief of the power and absolute supremacy of the "ma'arechet hakochavim," the order of the constellations, or the natural order. Hence, Pharaoh warns Moshe based on the statements of his astrologers that "evil" is "in the stars" for the Jewish people in the desert (Bo 10:10). Through His miraculous overriding of the laws of nature both in Mitzrayim and subsequently by protecting the Jewish people in the desert by sending supernatural Divine Clouds of Glory to shield K'lal Yisrael, Hashem indicated that He intervenes in Nature, shattering the myth of the supreme rule of "Natural Law" and underscoring His intense intervention in the world for the purpose of guiding the Destiny of His beloved people, descendants of the Patriarchs who originally merited this level of Divine intervention. It is for this reason that Sukkot, which commemorates this manifestation of Divine intervention, occurs in Tishrei, the month of the creation of the world, thus reminding us that the Creator of the natural order, overrides it at will for those who cleave to Him. (See also Defying Human Nature and Divine Miracles (TorahWeb.org, Parshas Vayeishev, 2001))
In the Hallel which we joyfully recite throughout the entire holiday, we state: "Rom 'al kol goyim Hashem. Mi Kashem 'Elokeinu haMagbihi lashaves, haMashpili lir'os bashamayim uva'aretz. M'kimi mei'afar dal..." (Tehillim 113:4-6) "G-d is exalted above all of the Nations. Who is like our G-d who dwells on High, but who lowers Himself to see in the heavens and the earth? Who raises up the downtrodden from the dust..." Malbim interprets this series of p'sukim in a manner which highlights the above-mentioned theme. For the "Nations of the World," G-d is the Creator alone, exalted in His Majesty, not concerned with the actions of mankind. The Jewish people, by contrast, recognize "our G-d" as One who, despite His exaltedness, interestedly observes and intervenes in the affairs of mankind guiding them toward their Destiny. (Also see Lonely Man of Faith (Chapter II), by Rav J. B. Soloveitchik zt"l.)
May the holiday of Sukkot serve as an impetus for all of us to recommit ourselves to Hakadosh Baruch Hu's mission for us in the world and thereby merit His constant, miraculous protection.