On the fifteenth day of this seventh month is the festival of Sukot, a seven-day period devoted to G-d.
Leviticus 23:34
The fact that Sukot is observed almost immediately after the holidays of Rosh HaShanah and Yom Kippur naturally associates it with them, and thus, besides its historical and agricultural significance, Sukot possesses a third level of significance, as the conclusion of the High Holiday period of the month of Tishrei.
Thus, on Sukot, as on Rosh HaShanah and Yom Kippur, we are meant to renew and revitalize our relationship with G-d, thereby eliciting the new and enhanced influx of Divine life-force particular to the new year.
The difference between the first two holidays and Sukot is that whereas during the former, we focus on G-d in ways that engender awe of Him, during the latter, we focus on Him in ways that engender love of Him.
Thus, what we accomplish on Rosh HaShanah and Yom Kippur through earnest, extended prayer and introspective contrition is accomplished on Sukot through joy.
--Daily Wisdom Volume 3