Even though the Day of Atonement is the only fast commanded in the Torah, the book of Zechariah mentions other fast days that Israel observed annually:

Thus says the LORD of hosts: The fast of the fourth month and the fast of the fifth and the fast of the seventh and the fast of the tenth shall be to the house of Judah seasons of joy and gladness and cheerful feasts. Therefore love truth and peace. (Zechariah 8:19)

In Zechariah’s day, there was a regular system of fasts on the calendar, which included a fast on the fourth month (Tammuz), the fifth month (Av), the seventh month (Tishrei), and the tenth month (Tevet). These observances began at times of Israel’s distress, and the Jewish community continues to observe them even to this day.

The seventeenth of Tammuz is a dark day on the Jewish calendar. It begins a three-week period of mourning that culminates with the ninth of Av, the fast day that commemorates the destruction of the Temple.

The seventeenth of Tammuz has several associations. In the days of the apostles, the Roman general Apostamos burned a Torah scroll and touched off rioting, which resulted in military reprisals. Some say that it was the original Torah scroll that Ezra the Scribe penned. Another tradition associates the seventeenth of Tammuz with an idolatrous image placed in the Temple. However, it is unclear whether this refers to an event that happened in Roman times or if it refers to the sin of King Manasseh. Traditional calculations find that on this day Moses descended from the mountain, found the Israelites engaged in idolatry, and broke the tablets of the Torah. The consequences of this sin reverberate throughout the generations. The Mishnah reports that it was on this date that Jerusalem under Nebuchadnezzar’s siege had run out of sheep, putting an end to the daily burnt offerings. One year later, the walls were breeched on the ninth of Tammuz. That was the day when the fast was originally observed (as mentioned in Zechariah 8:19). In the Second Temple Era, during the Roman siege of Jerusalem, the continual burnt offering ceased for the first time in several centuries on the seventeenth day of Tammuz, and prominent members of the priesthood surrendered and abandoned the Temple. Three weeks later, the Romans burned the Temple to the ground.

During the three weeks between the seventeenth of Tammuz and the ninth of Av, we mourn, fast, and pray for the rebuilding of the Temple. During this period of time, we should remember the Temple and the fall of Jerusalem and pray for the redemption with increased fervor. During the three weeks, devout Jews do not:

  • Conduct weddings
  • Play musical instruments or listen to music
  • Do any thing for which one should recite the Shehecheyanu blessing
  • Take haircuts or shave.

The Three Weeks should be a time of increased Torah study and giving of charity- in keeping with the verse, “Zion shall be redeemed by justice, and those in her who repent, by charity” (Isaiah 1:27). Specifically, we should study those portions of the Torah and the Prophets that deal with the building of the Holy Temple and those portions from the New Testament that speak about the spiritual temple of Messiah.

Source: First Fruits of Zion