Dora Bas Rivka Silver O'H
Zechariah looked up and saw four horns (horns as in "ox horns" as opposed to, say, trumpets). Zechariah asked what these horns represented and he was told that these likewise represent the various conquering nations: Babylonia, Persia, Greece and Rome. Then Zechariah saw four carpenters coming to saw down these horns. (These carpenters refer to various messianic figures including Moshiach himself, the Moshiach ben Yosef, Elijah the prophet and the Kohen Gadol.) The carpenters cut down the horns and threw them away.
Zechariah looked up and saw a man (an angel) with a tape measure in his hand. He asked the angel where he was going and the angel replied, to measure Jerusalem. Another angel came and told the angel with the tape measure not to bother because Jerusalem would be like an unwalled city, expanding ever outward because of the masses of people who would live there. If Jerusalem will be unwalled, how will it be protected? Don't worry, says G-d; He will be the wall around Jerusalem.
G-d tells the people of Judah to return from Babylonia, wherever they were exiled, and the people of the ten Tribes to return from the lands where Assyria has scattered them. G-d says that anyone who has injured the Jewish people injures himself. (This is a euphemism for saying that anyone who attacks the Jewish people actually attacks G-d.) G-d raises his hands and the nations who now oppress Israel will find themselves serving them; the nations will know that this came from G-d.
The rest of this chapter refers to the Messianic era when Israel will rejoice and G-d will dwell among them. Many nations will join Israel in the worship of the One G-d, Who will dwell in their midst. G-d will again choose Israel and Jerusalem and the rest of the nations will be silent when G-d takes this action.