The Kedushas Yisrael explains: On Sukkos we offer seventy bulls, corresponding to the seventy nations, as Chazal state. Each of these nations has the spiritual power to disturb the spiritual growth of Klal Yisrael. Each korban removes the power of one of the nations, bringing it into the realm of kedushah.
We reduce the number of korbanos each day of Sukkos to represent the decreasing power of the nations. However, this is only a surface removal of their power. Like with the achievements of Pesach we must return, and slowly and thoroughly achieve this properly. How so? Following Sukkos we begin a seventy-day period, each day representing another nation’s power decreasing, transferred to the realm of kedushah. When Chanukah arrives, we are left with eight out of those seventy days. Beis Shammai that we should do not begin counting anew, after all, we are counting down the nations just as have been counting down since Sukkos. In fact, these eight days are the most important as they correspond to the final, most powerful nations - those who can only be vanquished by dint of the neros Chanukah. During these days we fight the hardest against the evil in the world, to decrease the power of the yetzer hara. Finally, as we reach the eighth day - zos Chanukah - we finally complete the task of eradicating the tumah. The transfer to kedushah is complete.
