"And it shall come to pass in that day, that I will seek to destroy all the nations that come against Jerusalem. And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications..."
Now we have here an account of two remarkable works designed in that day. I. A glorious work of God to be wrought for his people: "I will seek to destroy all the nations that come against Jerusalem, v. 9. Nations come against Jerusalem, many and mighty nations; but they shall all be destroyed, their power shall be broken, and their attempts baffled; the mischief they intend shall return upon their own head. God will seek to destroy them, not as if he were at a loss for ways and means to bring it about (Infinite Wisdom was never nonplussed), but his seeking to do it intimates that he is very earnest and intent upon it (he is jealous for Zion with great jealousy, and has the day of vengeance in his heart) and that he overrules means and instruments, and all the motions and operations of second causes, in order to it. He is framing evil against them; when he seems to be setting them up he is seeking to destroy them. In Christ’s first coming, he sought to destroy him that had the power of death, and did destroy him, bruised the serpent’s head, and broke all the powers of darkness that fought against God’s kingdom among men and against the faithful friends and subjects of that kingdom; he spoiled them, and made a show of them openly. In his second coming, he will complete their destruction, when he shall put down all opposing rule, principality, and power, and death itself shall be swallowed up in that victory. The last enemy shall be destroyed of all that fought against Jerusalem. II. A gracious work of God to be wrought in his people, in order to the work that is to be wrought for them. When he seeks to destroy their enemies he will pour upon them the Spirit of grace and supplication. Note, When God intends great mercy for his people the first thing he does is to set them a praying; thus he seeks to destroy their enemies by stirring them up to seek to him that he would do it for them; because, though he has proposed it and promised it, and it is for his own glory to do it, yet he will for this be enquired of by the house of Israel, Eze. 36:37. Ask, and it shall be given. This honour will he have to himself, and this honour will he put upon prayer and upon praying people. And it is a happy presage to the distressed church of deliverance approaching, and is, as it were, the dawning of its day, when his people are stirred up to cry mightily to him for it.
-- Matthew Henry, from his Commentary, Zechariah 12:9-14