Why We Read the Seemingly Depressing Book of Ecclesiastes on Sukkot

Sukkot, which is the Feast of the Tabernacles that typically takes place around late September/early October, originally started as a harvest festival for the ancient Israelites. It is also referred to as זמן שמחתינו, or the "time of our joy," for a variety of reasons. Being the festive holiday it is, it comes off as a peculiar tradition [for Ashkenazi Jews] to read the Book of Ecclesiastes, also referred to as קהלת (Kohelet), during the Shabbat Sukkot services as a way to celebrate this rejoicing. The Book starts off with "Futility of futilities, all is futile (Ecclesiastes 1:2)" and continues with such lines as "for with much wisdom comes much grift, and he who increases knowledge increases pain (1:18)," "What does joy accomplish? (2:2)," and "for the fate of men and the fate of beast, they have the same fate...man has no superiority over beast, for all is futile (3:19)." It seems counterintuitive to read a dejecting text that points out the futility of life on a time where we celebrate the joy in our lives, so I did some research in hopes to resolve the paradox:

1. Let's not take it too far with the joy. Maimonides teaches the Aristotelian idea of the golden mean, which is to say that we should not take our מדות (character traits) to extremes. The trait of joy is no exception. In the Mussar text ארחות צדיקים ("The Ways of the Righteous"), if we give in entirely to humor or frivolity, we detract our focus from G-d. Ecclesiastes is the antidote to lightheartedness (Avudraham; R. Azaryah Figo). The joy we should feel is not for frivolity, but in serving G-d (Sefer HaMagid, Vol. III).
2. Joy is not about material wealth. King Solomon was a man who had hundreds of wives and concubines, as well as all the riches a man could imagine. At the end of the day, King Solomon realized just how transient material wealth can be, and how futile it was to chase after it (Ecclesiastes 1:11). We read Ecclesiastes at this time of year to remind ourselves that we are to rejoice in our lot, and that happiness will not be found in chasing after insane amounts of wealth (R. Mordechai Yaffe).
3. Ecclesiastes is about steadfastness to Torah. The Talmudic rabbis wanted to censor the Book of Ecclesiastes as apocryphal because its contradictory statements would end up confusing the masses (Shabbat 30b). However, the Rabbis decided not to suppress the text because the text begins with matters of Torah (Ecclesiastes 1:3) and ends with matters of Torah (Ecclesiastes 12:13). When discussing the question of "what profit does man have under the sun (1:3)," the Rabbis interpreted that as those who go "before the sun," i.e., study Torah, then one profits. In spite of the skepticism that King Solomon expresses throughout the Book, he concludes that the purpose of life is to "fear G-d, and keep His mitzvahs because that is the whole of man (12:13)."
4. Faith in the midst of uncertainty. In Ein Ayah, R. Avraham Yitzchak Kook points out that in spite of the intellectual pursuit, King Solomon ultimately returns to fear of G-d. Ecclesiastes is a reflection of how many people struggle with life. It can be confusing, contradictory, unfair, and downright harsh. As I wrote in a previous entry, faith is not acceptance in the form of passivity. We are allowed to question the purpose of it all and do so quite profoundly. At the end, of the day, we stick with G-d. We struggle, question, and wonder, and yet still remain within the framework of Judaism because the Jewish tradition allows for us to be human. The ability to stay steadfast to Judaism while still contending with the inconsistencies and injustices  of life that we observe and process with our rational faculties is the Ecclesiastical experience. It is to remind us that even in the unknown, we can still find meaning in life and experience joy. 
5. Accepting the transience of our physical lives. There is a Midrash (Shir HaShirim Rabbah 1:10) that says that King Solomon wrote this text at the end of his life, a time during which he reflected on all he had done. For King Solomon, he viewed life as a הבל (Ecclesiastes 1:2). The word הבל is commonly mistranslated as "futility"; a better translation would be "breath." For King Solomon, he realized that life was but a fleeting moment, and G-d was eternal. We can amass wealth and power, but there is an end for us. A definite, inevitable end. King Solomon realized this after all the wisdom and wealth he gained during his lifetime. It is my hope that we can not only realize the gift that life has to offer us and the important things in life, but to realize that the amount of time we have to enjoy and experience that life is like the length of a breath. People come, people go. The world in which we live is all too temporary. The sobering message that Ecclesiastes sends us is that we should enjoy and appreciate it while we still can. Having that level of radical acceptance to understand the ephemeral nature of life and how to fulfill your true calling within a small amount of time is the true joy of reading Ecclesiastes on Sukkot.