The Lord is going to cast off Judah and destroy the Temple. In judgement for their sin He will bring against Judah a fierce invader, namely the Chaldeans. The people have spurned God’s mercy, and so He will now be glorified in their judgement.
As with Judah in Habakkuk’s day, most people in our contemporary society remain recklessly indifferent to the fact of coming judgement. Our task is to grieve over them, and to confront the sin and unbelief all around us. We must be watchers, earnestly praying that God will work in power; we must be weepers, grieving over wickedness and the plight of the lost, and we must be workers, doing all that we can to preach the Gospel and bring sinners to the Lord Jesus Christ.