Zechariah 8:19 – Thus saith 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 joy and gladness, and cheerful feasts; therefore love the truth and peace.
The Fast of Tammuz, which we will celebrate this year on July 24, and the Fast of Ab on Aug. 14, mark off a season of mourning. The first fast reminded Jews of the day when the wall of Jerusalem was breached by the Babylonians in 587 B.C. (and later by the Romans in 70 A.D.). The second fast designated the complete destruction of the Temple and Israel carried off into captivity. The focus is on the idolatry that brought God’s judgment upon them, and a search to rid themselves of any idolatry within.
The medieval Jewish commentator Maimonides said that all these fasts would cease in the times of the Messiah. So Zechariah’s prophesy points to God’s final victory, which as believers we celebrate from our position as “seated with him in the heavenlies.”