After the destruction of the First Temple, the prophets instituted four fast days. These were meant to spur people to mourn the destruction and the exile, and thus to repent and correct the sins which caused these misfortunes. The fasts are: Asara Be-Tevet (the tenth of Tevet), Shiva Asar Be-Tamuz (the seventeenth of Tamuz), Tisha Be-Av (the ninth of Av), and Tzom Gedalia (the third of Tishrei). The Jews observed these four fasts during the seventy years of exile in Babylonia. When the Second Temple was rebuilt, these fasts were annulled and became joyous holidays. When the Second Temple was destroyed, the four fasts were reinstated.
These fasts are meant to inspire us to repent, to work to rebuild the Jewish people physically and spiritually, and ultimately to rebuild the Temple. Our Sages tell us that “Any generation in which the Temple is not rebuilt bears responsibility for its destruction” (since it would be rebuilt if we acted properly). We will now explain the significance of each of these fasts.