Chapter 12 stresses that when the remnant is regathered to the land they will rejoice. The two stanzas in this chapter are each introduced by the words ”In that day you will say“ (vv. 1, 4).
In that day (cf. 10:20; 11:10) refers to the time of deliverance which has been described in 11:1-12:6. When the nation is regathered and the Messiah is reigning the remnant, designated by the word I, will utter these words of praise. The remnant is distinguished from the nations, referred to in verse 4. In verses 1-3 God is praised because His anger has been turned away, Israel has been comforted (v. 1), and the Lord is (i.e., is the Source of) strength... salvation, and song. (”Salvation“ is mentioned at the beginning and end of v. 2.) Israel’s ”salvation“ will be more than spiritual peace of mind and deliverance; it will also include prosperity. To draw water from the wells of salvation (v. 3) pictures living according to God’s principles and thus participating with joy in the blessings He will provide.
12:4-6. The remnant will thank the Lord and will call on each other to let the world know what God has done, probably meaning what He will have done for Israel and Judah. God’s name (His revealed character) is to be exalted (vindicated) before the world, so that people everywhere will realize that He fulfills His promises. And people will sing to Him because of His glorious deeds.
The remnant also, will remind themselves of the greatness of God, the Holy One of Israel (cf. comments on 1:4). Being reassured that God is among them, they will be joyful (cf. 12:3). Chapter 12 is a fitting climax to the contrast between the fall of the Assyrian Empire, which was threatening Judah in Isaiah’s day, and the rise of God’s glorious kingdom, which will certainly come. Eventually all the world will know of God’s truth
Walvoord, J. F., Zuck, R. B., & Dallas Theological Seminary. 1983-c1985. The Bible knowledge commentary : An exposition of the scriptures. Victor Books: Wheaton, IL