Another thing, sing to God. (Isaiah 43:18) "Do not remember the former things" (ibid. 19) "Behold, I am doing a new thing" (ibid. 21) "This people I have formed for Myself" (ibid.) Thus said the Holy One, blessed be He: Just as I make these new things, so they said to Me to sing a new song. Therefore, it is said, "Sing to God a new song." And why did they see fit to say to sing with joy? Because they see and rejoice with Him, as it is said, "Let God rejoice in His works" (Psalms 104:31), and it is written, "Praise His holy name" (ibid. 105:3), and it is written, "Our soul waits for God" (ibid. 33:20).
The Holy One, blessed be He, said: You see Me and rejoice and reveal yourselves, and I also see you and reveal Myself and rejoice, as it is said, "I will rejoice in Jerusalem and delight in My people" (Isaiah 65:19). Therefore it is said, "Let them praise His name with dancing" (Micah 7:15), "As in the days of your exodus from the land of Egypt" (ibid.), as it is said, "And all the women went out" (Exodus 15:20).