Sukkot (and its appendage holiday, Shemini Atzeret) is eight days long, so it always falls on at least one Shabbat. Never able to resist the temptation to lengthen the service, the rabbis instituted the practice of reading the Book of Kohelet (that's Ecclesiastes to you). It's a longish book, and it usually adds about half an hour to the service, but it's one of my favorites.
Academics will tell you that Kohelet is a perfect example of ancient "Wisdom Literature," turning the book's author, King Solomon, into a earlier-day Poor Richard, without the poor. In fact, it's a Jewish "Carpe Diem," which on reflection risks turning the great King into Robin Williams. Nonetheless, it's a perfect counterpoint to Rosh Hashanah & Yom Kippur, where we spend the whole day reflecting on what we've done wrong. While "Unetaneh Tokef" reminds us that life is fleeting, and once it's gone, it's gone, "Kohelet" gives us a reason to care about living that life.
