Zechariah 9:11 As for you also, because of the blood of My covenant with you, I have set your prisoners free from the waterless pit.
vs 12 Return to the stronghold (or Stronghold), O prisoners who have the hope (or prisoners OF hope); This very day I am declaring that I will restore double to you.
In Joel we saw God's promise to restore all that was taken by every type of locust mentioned, whether stripping, gnawing, flying etc. God said He would give back to Israel all that was taken.
Here in Zechariah we see God talking, not just about restoring their freedom because of the blood of His covenant, but even beyond that. He's talking about restoring double.
Note in verse twelve the prophet calling the prisoners to the Stronghold, or place of safety. He calls them the prisoners who have a hope, or prisoners who, even though they have been/are captive, they are not without hope.
Not only do they have hope. But by the end of verse twelve they have a promise of double restoration. A promise from God will keep.