Zechariah 8: fasting as a sign of joy

In Zechariah 7, people from Judah asked if they should fast as in Babylon in order to show sadness in exile. In Zechariah 8 we read:

18-19 Again I received a Message from God-of-the-Angel-Armies:
“The days of mourning set for the fourth, fifth, seventh, and tenth months will be turned into days of feasting for Judah—celebration and holiday. Embrace truth! Love peace!

The days of mourning will become feasting days, besides:

20-21 A Message from God-of-the-Angel-Armies:
“People and their leaders will come from all over to see what’s going on. The leaders will confer with one another: ‘Shouldn’t we try to get in on this? Get in on God’s blessings? Pray to God-of-the-Angel-Armies? What’s keeping us? Let’s go!’
22 “Lots of people, powerful nations—they’ll come to Jerusalem looking for what they can get from God-of-the-Angel-Armies, looking to get a blessing from God.”

The Lord didn't call Israel to be a super country, living as rich man isolated in his castle. The Lord called Israel to be a blessing to all nations. Jerusalem will gather people form many countries who seek the blessing from God.