The period of teshuvah ushered in by Rosh Hashanah appears to end dramatically with the blowing of the shofar at the culmination of Yom Kippur. The holiday of Sukkot that follows appears to be independent of the days that precede it. Indeed, Sukkot presents quite a sharp contrast to Yom Kippur. Rambam characterizes Yom Kippur as a day lacking in "simchah yeteirah"(hil. Hanukah 3:6), while he depicts Sukkot precisely as a time of "simachah yeteirah" (hil. Sukkah 8: 12). However, the fact is that according to many halachic sources, the final "gemar" with respect to man's status is not until Hoshanah Rabah, the conclusion of Sukkot. Moreover, compelling parallels bind Yom Kippur and Sukkot and there are strong indications that the intervening period is not merely a bridge between them, but constitutes a significant period by virtue of the link between them.
In Sefer Devarim, Tehilim, and elsewhere we find references to avodat Hashem be-yirah, particularly accented by Yom Kippur, as well as to avodah be-simchah, projected by Sukkot. The midrash in Tehilim, commenting on these distinctive approaches reflected in Tehilim chapters 2, 100 questions the relationship between them: "im be-simchah eich be-yirah, ve-im be-yirah eich be-simchah?" One view in the midrash perceives the "yirah" as a method employed in this world to achieve the ultimate reward of "simchah" in the World to Come. Others argue that "yirah" and "simchah" are simply distinctive approaches to man's relationship with Hashem. However, Tana De-bei Eliyahu (no. 3) projects a mutually enhancing impact: "amar David ha-Melech yirati mitoch simchati, ve-simchati mitoch yirati". It is possible that this approach also characterizes the relationship between Yom Kippur, the holiday of yirah, and Sukkot, the festival of simchah.
A careful reading of Parshat Emor reveals several parallels between these two moadim. The term "ach" (Vayikra 23:27, 39), connoting something different or exclusive is used only regarding these two holidays. The term "mikra kodesh" which is the common theme of all the holidays delineated in the parshah is treated in an unusual manner with respect to Yom Kippur, as it does not connect to the general prohibition to do work on a festival, as with other moadim, but to the specific expression of fasting on this day. Sukkot's treatment in Emor is also unique. The Torah records a second account of this holiday which includes reference to the lulav but omits the term "mikra kodesh". In both Yom Kippur (23:28-"ki yom kipurim hu le-chaper aleichem") and Sukkot (23:43-"lemaan yeidu doroteichem ki be-sukkot hoshavti et benei yisrael behozii otam me-eretz mizrayim"), the Torah feels the need to justify the holiday. The term "lifnei Hashem Elokeichem"(24:28, 40) appears in connection with each of these events. Ibn Ezra and Seforno allude to the apparent link between Yom Kippur and Sukkot rooted in some aspects of their unusual treatments.
It is possible that the Torah conveys by means of some of these parallels that the themes of "yirah" and "simchah" are each critical components of a comprehensive avodat Hashem, and that each enhances the other when implemented properly. The role of yirah as preceding wisdom and Torah knowledge is well documented. Simchah, too, is critical for the study of Torah ("pikudei Hashem mesamhei lev..."), for the attainment of prophecy (Shabbat 30b), and plays a role in many other halachic norms, as well.
Yom Kippur and Sukkot contrast in ways that accent the parallels between them. The exemption of miztaer, the expanded role of halel, the motif of "teshvu ke-ein taduru", for example, reflect an extreme manifestation of simachah. The motif of inui, a full complement of issur melachah, and a rejection of halel accentuate the yirah of Yom Kippur. Each extreme plays an important role in the overall balance represented by the different moadim, reflecting the broad spiritual ambition of halachic life itself.
The Rishonim questioned why Sukkot is not celebrated in context of yeziat mizrayim which it celebrates? The Ramban (Emor, ad loc) and Tur (beg. of hil. Sukah) address this question. They posit that weather conditions during the period of Nissan would not have properly accented the normative aspect of Sukkah. However, the Zeror Hamor and Aruch Hashulchan suggest that the Torah deliberately linked Sukkot with Yom Kippur for thematic reasons!
The Shulchan Aruch rules that tachanun is not to be recited in the period between Yom Kippur and Sukkot. The Beit Yosef (no. 131) eplains that this is the period in which the Beit Hamikdash will be completed. The Aruch Hashulchan (524:7), however, posits that this ruling is connected to the period of simchah that follows the aftermath of Yom Kippur, and characterizes the entire intervening period until Sukkot as "yemei simchah". One may speculate that the appropriate time to complete the mikdash is in this period precisely because of this status, particularly if this period symbolizes the integration of simchah-yirah which is especially indispensable to the proper functioning of the Beit Hamikdash.
The obligation to begin the process of building the Sukkah immediately after Yom Kippur is formulated twice in the Shulchan Aruch: in the last halachah of hil. Yom Kippur and, again, in the first halachah of hil. Sukah. While the commentators struggle to explain the differences between the two contiguous formulations, it remains difficult to fathom why this law (or laws) could not be articulated in one place. In light of our brief analysis of the complementary relationship between the two extreme manifestations of yirah and simchah, we can perhaps further appreciate the precision of these formulations. Yom Kippur is significantly enhanced by anticipating the upcoming festival of "u-semahtem lifnei Hashem Elokeichem shivat yamim". Immediate involvement with the Sukkah is, indeed, a most fitting culmination to hil. Yom Kippur. At the same time, the themes of Sukkot take on greater meaning against the framework of "ki Yom Kippurim hu le-chaper aleicheim lifnei Hashem Elokeichem". Thus, hil. Sukkah, itself, demands that the process of building the Sukkah be initiated in the immediate afterglow of teshuvah, selichah, kapparah and yirah.