This Shabbat is different from the others. Obviously, each Shabbat has its own particular energy, a combination of the day of the month, the time of year, and the Torah portion(s) being read. However, this Shabbat has an additional, different component: it is the 17th of Tammuz. Our sages recount that five events occurred on that day throughout Jewish history that led our prophets to decree a day of fasting. When this fast falls on Shabbat, it is deferred until Sunday.
The events of the 17th of Tammuz were:
1) Moshe broke the tablets after descending from Mount Sinai, where the Jewish people, only forty days after receiving the Torah, were worshipping the Golden Calf.
2) The walls of Jerusalem were breached during the time of the First Temple. Three weeks later, it was destroyed by the army of Nebuchadnezzar, king of Babylon.
3) During the time of the Second Temple, services were interrupted. Again, three weeks later, it would be destroyed by the Roman army led by Titus.
4) There was a public burning of the Torah, carried out by Apostumus the wicked, a Roman general in the time of the Second Temple.
5) An idol was placed in the Temple to be served instead of God.
Our sages say that God arranges "bad" events for "bad" days, so to speak. The truth is that these days, being days of fasting, have a very special potential that remains valid even when they occur on Shabbat and the fast is postponed until Sunday.
When fasting falls on a weekday, the way to connect with the energy contained within the day is through the act of fasting itself. It is such a profound energy that it cannot be accessed through positive action or doing something; rather, it is the opposite: by ceasing to act, by abstaining from doing things, one can reach the special essence of the day.
But when fasting occurs on Shabbat, since that energy is available and increased by the very holiness of Shabbat, the way to connect to it is through the pleasures of Shabbat: food, drink, etc.
This is similar to what will happen in the Messianic era. Today, God's presence is so overwhelming that the world is not prepared to bear it. That is why God, so to speak, conceals Himself to allow the world and its inhabitants to exist. In the Messianic era, God's presence will be revealed, and yet the world will continue to exist, thus combining these same two opposites: an incredibly powerful energy that can be perceived through everyday actions, such as on the fasting day that occurs on Shabbat.
May God quickly transform these days of sadness into days of joy and rejoicing, with the coming of our righteous Messiah, now!.