Atzeres

Why is the 8th day of Sukkos referred to as an "Atzeres", a stoppage?

The Netziv in Ha'amek Davar explains that the primary purpose of the mitzvah of aliyah l'regel is to become inspired by seeing the function of the Beis HaMikdash up close and coming in contact with the kohanim and the levi'im, who served an educational role within the nation. On Sukkos, it is easy to lose sight of this greater goal within the numerous special mitzvos and observances of the week - sukkah, lulav, aravah, and simchas beis ha-sho'eiva. On the 8th day, though, all of these mitzvos cease, and a person is able to stop and think deeply about everything that he's seen over the course of the week and to take out of it specific lessons and a general commitment to improve his avodah that will last through the entire year.