Charles Spurgeon Commentary Zechariah 8:19

"Thus saith Jehovah 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 truth and peace." — Zechariah 8:19 (ASV)

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 joy and gladness, and cheerful feasts; therefore love the truth and peace.

Here is an answer to more than they asked for. The messengers only inquired about one fast—what they should do with it—namely, the fast of the fifth month; but they get instruction on three other fasts. If you come to God's Word on any point, you will not only be resolved on that point, but you will be guided in many other ways, for God's Word is full of instruction, and those who are willing to be taught by it will become wise in all ways. So now they are told that these fasts were to be turned into feasts.