The second night vision is short and, to those returned exiles, probably very sweet. "Horns" in the Bible represent power and especially military strength. To cut off a nation's horn is to render it powerless against attack. God here is promising them that the "four horns" which scattered his people will be destroyed.
Who are the four horns? That is a source of debate among the scholars, but I would think that Assyria and Babylon are two of them—it only makes sense. But once again, it's that number "four" that may be the key. Israel had enemies on every side. Even during the siege of Jerusalem there were allies who were no help to them (Egypt) and old enemies that actively aided the Babylonians against them (Edom). Perhaps the meaning is this: all of their enemies on every side (north, south, east, and west) would be punished for their part in the destruction of Judah, and especially Jerusalem and the Temple.
And who are the "smiths" in the vision? Just as a smith is an artisan who creates and mends, these are the people who would carefully and selflessly work to put back together the nation. I have never seen a list of possible names, but it seems to me that Ezra, Nehemiah, and the three post-exilic prophets—Haggai, Zechariah himself, and Malachi—should be included.
God is once again telling these people that he knows what they are going through and that he cares. But added to that, he is promising judgment on the wicked for their part in Judah's suffering. He is also promising that His people will have what they need to repair themselves and become that promised, glorious, restored kingdom that every one of the prophets spoke of.
And for us? Most of us have never felt severe physical persecution. The worst we have had is a bit of name-calling or being left out of the popular crowd. But do not think it won't come. Our country is moving in a direction where we may begin to feel the heat in our own lifetimes and our children and grandchildren may suffer real persecution.
God tells us that it is not our place to exact vengeance (Rom 12:19). However, He has always promised that He will take vengeance for his people (1 Sam 24:12; Psa 58:10,11; Isa 61:2; 2 Thes 1:6-8, etc.). He will not allow our suffering to go unrequited.
And He also gives us the promise that we will have what we need in this glorious restored kingdom of the Messiah, the church--to equip the saints for the work of ministry, for building up the body of Christ, (Eph 4:11-16). Look around at the "smiths" you have among you, who work for little or no remuneration, who give of themselves for hours upon end to teach the ignorant, to heal the broken, to lead the flock, and you will see the hand of God working among you. If we don't see it, it is only because, like so many of those people long ago, we aren't looking for the right things. We can be certain that God will not fail us.
When he opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the witness they had borne. They cried out with a loud voice, “O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?” Then they were each given a white robe and told to rest a little longer, until the number of their fellow servants and their brothers should be complete, who were to be killed as they themselves had been. (Rev 6:9-11)