In the year that the Israelites left Egypt, on the 17th day of Tammuz, Moses descended from Mount Sinai to find the Jewish people dancing around the Golden Calf. In exasperation, Moses threw down the two tablets of law given to him by God, smashing them.
During the centuries that followed, the 17th of Tammuz continued to be an inauspicious day for the Jewish people, a day on which great tragedies occurred. It therefore became a day of fasting and repentance from sunrise to sunset.
One such tragedy that occurred on the 17th of Tammuz was the cancellation of the daily offerings in the First Temple. This offering, known as the tamid (constant), is first mentioned in Numbers (28:3-4,6): “This is the fire offering that you will bring for God: unblemished he-lambs in their first year, two each day, for a continual burnt-offering. One lamb you will offer in the morning, and the other lamb you will offer at dusk ... It is a constant burnt-offering, which was offered on Mount Sinai, for a sweet savor, an offering made by fire for God.”
When the Babylonians began their siege of Jerusalem, the Jews still had enough livestock within the walls to maintain the tamid offering. As the siege continued, however, the priests of the Temple struggled to maintain the Temple service. They even sent baskets of silver and gold over the wall to buy sheep for the offerings from the Babylonians. On the 17th of Tammuz, however, the basket was returned to them empty – there were no more sheep to be purchased, and so the daily offerings came to an end. Needless to say, the cessation of the daily offering was a significant blow to the morale of the people of Jerusalem and the entire nation.