The mishnah (Sukah 48a) determines that while one should not completely dismantle the sukah on the seventh day of Sukkot in advance of Shemini Azeret, one should begin transferring out the utensils that established the sukah as the primary residence during the week of Sukkot. The Rambam (Hilchos Sukah 6:11,14) codifies this halachah. The Ra'vad speculates that this preliminary evacuation of the sukah is limited to circumstances in which one will be eating in the structure on Shemini Azeret and is designed to preclude the prohibition of baal tosif. However, the mishnah and Rambam make no allusion to these conditions. It seems that departing from the sukah in anticipation of Shemini Azeret ("le-kevod yom tov ha-acharon") is an important element in the transition from Sukkot to Shemini Azeret! A brief analysis of some of the salient features of Shemini Azeret may serve to clarify this prerequisite.
It is evident from the pesukim in parshat Emor, and Pinchas that Shemini Azeret is both a continuation and culmination of Sukkot, as well as an independent hag. This dual status is reflected by the totally different configuration of the korbonot and by the unique halachot signified by the acronym "PZRKShV" (Sukah 48a) that govern this day. While Shemini Azeret is ideally referred to by its own designation- "ha-shemini chag ha-Azeret ha-zeh", many poskim conclude that the designation "chag ha-Sukkot" is also effective, obviating the need to repeat the shemonah esrei or birkat ha-mazon. Shemini Azeret certainly serves as part of the extended period for the korban chagigah of Sukkot. It appears that Shemini Azeret precisely because of its singular character is the perfect conclusion to Sukkot!
The Seforno notes that the transition to Shemini Azeret is particularly striking as the holiday in which there are two distinct mitzvot - lulav and sukah is followed by or even concludes with a yom tov which focuses exclusively on tefilah and Talmud torah, the staples of year-round halachic observance. It is also significant that the keriat ha-Torah of Shemini Azeret (parshat Re'eh) only obliquely alludes to Shemini Azeret ("ve-hayita ach sameah", as understood by Sukah 48a). The reading concentrates on the mitzvot of zedakah etc. that apply all year. Only the 3 regalim are explicated in these sections. Perhaps it is precisely the concentration on year-round themes and the de-emphasis of particular festival themes on this unique day that qualifies Shemini Azeret as the perfect culmination of Sukkot and the entire period that begins with Rosh Hashanah.
After the intense religious experiences of Rosh Hashanah and Yom Kippurim it is inconceivable that one could simply revert to routine life. Moreover, the charged environment and process of introspection engendered by the Yomim Noraim provide an opportunity for further spiritual advancement that should be capitalized upon. And yet, the ultimate goal is to integrate the impact of the Yomim Noraim experience into an upgraded daily halachic life. (See, also, Maharsha, conclusion of massechet Megillah.) Thus, one ideally begins to build the sukah immediately after Yom Kippur. It is important to take the experience of the kodesh ha-kodoshim and to apply it to one's own dwelling, but this requires a more vulnerable and temporary structure that is evidently reliant upon Hashem's hashgachah (Divine Providence). Many of the dimensions of the Sukah are patterned on the Beit ha-Mikdash itself, and at least the sechach is muktzah le-mitzvato (used exclusively for the mitzvah) for the entire holiday.
The first halachah recorded in the Shulchan Aruch regarding Sukkot is the disqualification of a Sukah under the roof of one's home. The Taz explains that there should be nothing intervening between the Sukah and the heavens, undoubtedly symbolizing the direct relationship and reliance upon Hashem. The Magen Avraham emphasizes that the very objective of the sukah is the departure from one's permanent home. The fact that the sukah ideally is a 7-day structure meant to house all major activities of the week- eating, sleeping, social interactions etc.- reflects the importance of this total relocation. The Rama notes that one should conduct oneself in the sukah in a manner befitting a mitzvah, although the range of activities should parallel one's real home. The poskim explain that one should avoid anger or idle gossip and increase Torah study. The Sukah should be a real home, but one in which idealized standards are practiced, as befitting post-Yomim Noraim developments!
And yet, one must ultimately return to one's permanent abode and routine. Moreover, the goal of the holidays of Tishrei is not to escape and abandon daily life, but to inspire and secure its elevation. After 7 days of intense additional avodat Hashem highlighted by both the sukah and 4 minim, one is sufficiently fortified and spiritually revitalized for a triumphant reintegration with the challenges of daily life.
Shemini Azeret is the appropriate culmination to Sukkot precisely because it is finally time to relinquish the lulav and sukah and to give full concentration to the spiritual staples of Talmud torah and tefilah. Thus, this day is both an indispensable component of Sukkot and an independent hag. Anticipating the transition to Shemini Azeret, we already begin to dismantle parts of the environment of the sukah, declaring that we have successfully assimilated the idealized framework of that structure and are confidently poised to return to our more permanent structure having achieved spiritual renewal and reinforcement. The Torah reading only alludes to Shemini Azeret, instead focusing on tzedkah and other year-round challenges that are, ironically, more relevant to this decompression from Sukkot and significant transition to the rest of the year. The commemoration of Simchat Torah, in which we conclude and renew the Torah cycle accentuates this theme, as well. The theme and method of observance of Shemini Azeret is simple and straightforward. However, the significance of this day as the culmination of the Yomim Noraim and Sukkot and as the transition to the rest of the year is profound and ambitious. For this reason, Shemini Azeret is a day of unvarnished simchah: "vehayitah ach sameach".