While it is a commandment to be joyful at all times, there are exceptions to this rule; certain times are designated on the Jewish calendar for mourning and repentance. In Judaism, there are five public fast days throughout the year; most of them are connected with mourning the destruction of the First and Second Temples and the invasion of Jerusalem and the entire Land of Israel by the Babylonians in the 5th century BCE and the Romans in 70 CE. The first exile, called the Babylonian exile, lasted only 70 years. However, the second exile, which began when Jews lost control of Judea to the Romans, has lasted for over 2,000 years now, and it is the exile from which we are currently praying for deliverance. The Rambam (a great Torah sage who lived at the time of the Spanish Inquisition) has told us that we should look forward to the coming of the Messiah every day, even during these days of mourning, and we should long to return toJ Jerusalem, and that the Holy Temple should be rebuilt.
Like the most profound day of mourning on the Jewish calendar, Tisha B’Av, there are many disasters that occurred on the 17th of Tammuz that give us reason to mourn; it was on this day that Moses descended from Mt. Sinai after spending 40 days receiving the Torah directly from Hashem, only to see the people engaged in pagan worship of the Golden Calf. He smashed the stone tablets which contained the Ten Commandments. Hundreds of years later, King Menashe put up an idol in the Holy Temple on the 17th of Tammuz. Apostmos, a Greek general, burnt the Torah scroll. Daily sacrifices ceased on this day, and the Romans breached Jerusalem’s wall in 70 CE, which was the beginning of the second exile.
This fast marks a period between the 17th of Tammuz and Tisha B’Av known as “The Three Weeks.” During this time, we do not celebrate weddings or buy new (fancy) clothes. It is a time to ask for G-d mercy and to repent for our misdeeds and for the sake of the entire Jewish People.