The justice of God is demonstrated when he punished Assyria for her haughty pride against Israel. As usual, the nations do not realize that is because God allowed them to get the victory, that they actually overcame the Israelites. (10:5-19)
Chapter 11 is the glorious description of the coming of the Messiah and the final restoration of the people of Israel. Chapter 12 is a thanksgiving and praise song, which express the gratitude to God for his great care for his people. God is described as the source of salvation and security.
I think that this song is also an extraordinary effort from Isaiah to demonstrate to the Israelites that, if you approach life with God presence and God’s view, your life as individual or as nation could be much better. You do not need human alliances to save or bless your life; you need the Holy One of Israel.
This song of praise is also a reminder that the same God who helped the Israelites in the past will help them now in the present, and will help them in the future. The prophet says: “Sing praises to the Lord, for he has done gloriously; let this be known in all the earth” (12:5)
Do not forget that God has a remarkable “record” of faithfulness for his people, and every time that you praise him for what he has done in or through your life, is also a proclamation that he is going to do more now and in the future.
That is why we can sing with the Israelites: “Shout aloud and sing for joy, O royal Zion, for great in your midst is the Holy one of Israel” (12:6)