(Isa. 12:1)
The Targum says, “I sing because although when I had sinned You were angry with me, yet, when I returned to Your law, You showed me mercy.” Rashi: “I sing because my exile was an atonement for my sins.” The thought expressed by Rashi is analogous to that in Psalm 119:71: “It is good for me that I have been afflicted for thus have I learned Thy precepts.” Kimchi says, “The reason for my singing is that You did not let me remain in the exile, as I had deserved.”
(Solomon B. Freehof, Book of Isaiah [New York: Union of American Hebrew Congregation, 1972), 81.)