Parashat Pinchas lists the Korbanei Musaf for the various holidays throughout the year. The Korban for Sukkot is unique; thirteen bulls are sacrificed on the first day, twelve on the second, and the pattern continues with one fewer bull each day until the seventh day in which seven bulls are sacrificed; when Shemini Atzeret arrives, one bull is brought. The Gemara in Sukkot (55b) explains that the total number of bulls brought on Sukkot is seventy, to represent and protect the seventy original nations of the world. The Korban brought on Shemini Atzeret represents one nation—Bnei Yisrael. However, why not bring ten bulls each day, instead of different numbers? Perhaps we should have a new excitement for every day of the Chag, and in order to generate the excitement, we must have a new number of bulls every day. In that case, why do we count down from thirteen bulls to seven and not count up from seven to thirteen? A basic approach suggests that counting down represents the gradual weakening of the other nations. Taking a more advanced methodology, others relate this process to Matan Torah. The Midrash teaches that before Matan Torah, Hashem offers each of the seventy nations the Torah, only to have His offer refused. Each day of Sukkot, Hashem offers the Torah to more and more nations until all of them refuse. As a result of this refusal, we conclude with the number seven, since it represents the number of Mitzvot with which the other nations were left after they rejected the Torah—the Sheva Mitzvot Bnei Noach.
Each day of Sukkot brings us closer to the day when Hashem chooses Bnei Yisrael, which adds new Simcha to each following day of Sukkot. Finally, our happiness climaxes on the eighth day—Shemini Atzeret—when we celebrate the Torah. We hope that this year, we will be able to celebrate our reunion with Hashem and bring all the Korbanot in the Beit Hamikdash, BiMeheira VeYameinu.