Zechariah 8:14
For thus saith the LORD of hosts; As I thought to punish you, when your fathers provoked me to wrath, saith the LORD of hosts, and I repented not: For thus saith the LORD of hosts; As I thought to punish you, when your fathers provoked me to wrath, saith the LORD of hosts, and I repented not:
The verse looks back to the time when God formed a settled purpose to punish Judah because their fathers provoked Him to wrath, and He did not turn back or relent from carrying out that judgment. It carries the implication that Israel had been tested and cared for by God, yet had failed to fulfill His purposes for them.
Read with the verse that follows it, it sets that former unrevoked judgment in direct contrast with God's present purpose to do good to Jerusalem and to Judah. That contrast is given to remove fear and to call the people to be strong.
The surrounding promises unfold what that doing good means, that God would return to Zion and dwell there, that Jerusalem would be restored as a city of truth and as the holy mountain, and that He would save Judah and Israel so that instead of a curse they would become a blessing. As surely as the earlier purpose to punish was not revoked, so the present purpose to do good to Jerusalem will likewise not be revoked.
That promised restoration points to a spiritual restoration for Israel to take place before the end of time. The assurance that God intends good to Jerusalem and Judah is therefore encouragement for sincere missionary work for the Jews.