I am writing this on Sunday, 22 July. The day after tomorrow is Tisha b'Av, the ninth day of the month of Av on the Jewish calendar.
Tisha b'Av is a fast day, one of six on the Jewish calendar. On Tuesday, the fast will run from about 7:45am to 8:15pm. During the fast, we are not to eat or drink, listen to music, or be intimate with a spouse. It is a time of mourning, for historically, the two Temples in Jerusalem were both destroyed on Tisha b'Av, and even after 1900 years, we remember, and we mourn the loss.
Traditionally, observant Jews will gather in the synagogue the evening before the fast (the day begins at sundown on the Jewish calendar, so while the fast is on a Tuesday this year, Tisha b'Av actually begins at sundown on Monday) to read Eicha, the Book of Lamentations. The Lamentations are read sitting down on the floor, by candlelight, in an otherwise darkened room. The chanting goes to a very sad melody. While I can't say that I like Tisha b'Av, I've always been deeply moved by the reading of Eicha; my Hebrew is not good enough to follow the reading, and I am not familiar with the Book in English, but it still touches me every year.
This deeply moving reading is followed the next day by the Fast. I have always felt something deeply spiritual about the observances of this day. The public reading of the Lamentations, a formalized, ancient, poem of deep sadness, is followed by the very private ritual of fasting the next morning. It's a one-two punch that drives home the true sadness of the day.
I have said before, and I meant it, so I'll say it again, that Judaism is not an ascetic religion. We are not supposed to deny ourselves the pleasures of the world, nor are we supposed to spend our days in sadness. Rather, the good things in life are taken in moderation, because they really can make life worth living.
But sometimes, there are ascetic days in Judaism. Those, too, are taken in moderation. There's an essential recognition in Judaism that it's OK to mourn, and OK to remember the tragedies of the past, but also that we cannot dwell on them. As usual in Judaism, life is for the living, and is meant to be lived.