Albert Barnes Commentary Zechariah 8:15

"so again have I thought in these days to do good unto Jerusalem and to the house of Judah: fear ye not." — Zechariah 8:15 (ASV)

So have I turned and purposed in these days to do well unto Jerusalem - Dionysius: “God, to be better understood, speaks with the feelings and after the manner of men, although, in the passionless and unchangeable God, there is no provocation to anger, nor turning, implying change in Himself.” So He says by Jeremiah, I know the thoughts that I think toward you, says the Lord, thoughts of peace and not of evil (Jeremiah 29:11). And, with the same contrast as here, As I have watched over them to pluck up and to break down and to throw down, and to destroy and to afflict, so will I watch over them, to build and to plant, says the Lord (Jeremiah 31:28). His having done what He purposed before was all the more a pledge that He would do what He purposed now.

His chastisements were the pledges of His mercies, for they too were an austere form of His love. Osorius: “When the Lord stretches out His hand to strike those who are defiantly disobedient in guilt, none can hold His hand to prevent Him from exacting the due punishment. Therefore He says that He did not repent; so, when He receives into grace those who repent of their sins, no one can in any way delay the course of His benevolence. For the gifts and calling of God are without repentance (Romans 11:29).

And to the house of Judah - Ribera: He speaks to the two tribes, not to or of the ten, because Christ was to come to the two tribes, and Zechariah was prophesying to them. They were to be admonished to prepare themselves in good works, lest the coming of Christ fail to profit them on account of their depraved ways. But the ten tribes were far off in the cities of the Medes, and Christ was not to come to them; instead, they were to hear the Gospel through the Apostles. And so Zechariah prophesies of the conversion of all to the glory of Christ, yet he could not admonish all, but only those to whom he was sent.