Both mitzvos associated with the holiday of Sukkos, taking the daled minim as well as dwelling in the sukkah, represent achdus - unity. The Medrash compares the esrog, which has an appetizing taste and a pleasing aroma, to Jews who possess both Torah learning and the performance of mitzvos; the lulav, the date palm, which has a sweet flavor but no fragrance, to Jews who learn Torah but lack good deeds; the hadasim, the myrtle, which has an appealing smell but no taste, to Jews who perform mitzvos but are devoid of Torah learning; and the aravos, the bland and odorless willow, to Jews who possess neither Torah learning nor good deeds. We bind all these species together to underscore the necessity of uniting all Jews under the collaborative banner of serving the Ribbono Shel Olam. Similarly, the Gemara (Sukkah 27b) derives from the pasuk, "Every citizen in Yisrael shall dwell in sukkos" (Vaykira 23:42) that all the people of Israel could theoretically dwell in one sukkah, for the sukkah need not be the private property of those sitting within it. Undoubtedly, all of Klal Yisrael inhabiting one sukkah, coexisting under the same roof for seven consecutive days, would be a powerful statement of solidarity and achdus.[1]
Why is Sukkos uniquely suited to forging and reinforcing the bonds of achdus? What aspect of the holiday dovetails with the general notion of unity? Rav Avrohom Schorr (Halekach Ve'halibuv) suggests that the answer is tied to the historical roots of the holiday itself.
According to one view in the Gemara (Sukkah 11b), the sukkah corresponds not to the actual tents used by the Jewish people on their way out of Mitzrayim, but to the Clouds of Glory - the ananei hakavod, that accompanied them and hovered overhead as they traveled throughout the desert. Either way, the Tur (Orach Chaim 625) wonders why the holiday of Sukkos is celebrated in the month of Tishrei and not in Nissan, when Klal Yisrael actually exited Mitrzayim and entered the midbar. The Vilna Gaon (Shir Hashirim 1:4) explains that in the wake of the sin of the golden calf, the luchos were broken and the ananei hakavod dispersed. Immediately after Yom Kippur, when Hashem forgave the Jewish people and Moshe descended with the second set of luchos, the command to create the Mishkan was issued. In the days that followed, the people set about gathering and collecting materials, and on the fifteenth of Tishrei, construction began. With the commencement of the building of the Mishkan the Clouds of Glory returned. Sukkos marks not the initial appearance of the ananei hakavod, which occurred in Nissan, but their homecoming and restoration on the fifteenth of Tishrei following the sin of the golden calf.
In general, the ananei hakavod reflect achdus in Klal Yisrael. The Gemara (Taanis 9a), attributes the existence of the ananei hakavod to the merit of Ahron Hakohen who was known for his pursuit of peace and love for mankind (Avos 1:12). Hence, when he passed away, they too ceased to function. Perhaps the model for achdus is the Clouds of Glory, because just like in a gas or a cloud, the intermolecular forces are weak, enabling the molecules to move about freely within the container, so too the ideal form of achdus is a supportive and inclusive network that does not restrict individuality or demand uniformity.
The presence of the ananei hakavod was affected by the sin of the golden calf because it entailed an element of division and discord. The Beis Haleivi (Parshas Mishpatim) notes that in truth, only a small group participated in the sin of the golden calf directly, as the pasuk states, "there fell of the people that day about three thousand men" (Shemos 32:28). For this reason, when the golden calf was built and handed over to the unruly mob, they were told "here are your gods" (Shemos 32:4), not "our gods", for everyone else was not particularly invested or interested. However, they all became implicated as a result, and the sin of the golden calf remains a stain on the consciousness of the Jewish people for all generations (Rashi, Shemos 32:34), not because of the act that was perpetrated by a small subset, but because the majority was indifferent to the idolatrous minority in their midst. Discounting the folly of the few as sins of the "other," and tolerating the emergence of "your gods" alongside "our God," fractured the community of the Jewish people and chased away the ananei hakavod.
As a response, the directive to establish the Mishkan, which demanded a coordinated effort to elicit donations and expertise from all sectors of the Jewish people, was intended to heal the divisive wounds left by the golden calf and sow the seeds of unity once again. Indeed, the Mishkan was referred to as the "Mishkan of Testimony" (Shemos 38:21), for the Mishkan "was a testimony to Yisrael that Hashem had forgiven them for the incident of the golden calf" (Rashi). On the fifteenth of Tishrei, once the Mishkan project was underway, the ananei hakavod returned as a symbol of the renewed spirit of achdus that was sweeping through the Jewish camp. According to the Medrash (Tanchuma, Naso 25) the Mishkan brought shalom - "peace" back to the Klal Yisrael, and this phenomenon is commemorated on holiday of sukkos which is suffused with the theme of achdus, and embodied by the sukkah itself which is often called in our prayers "sukkas shalom" - "the sukkah of peace." May our celebration of sukkos this year inspire and ignite a greater sense of unity amongst our people and precipitate an era of prolonged peace and security.
[1] It seems that these two symbols of achdus correspond to two distinct forms of unity, see The Unity of the Sukkah and the Daled Minim.