Sing to the LORD a new song, for He has done marvellous things; His right hand and His holy arm have worked salvation for Him. The LORD has made His salvation known and revealed His righteousness to the nations. Psalm 98:1-2
When Christians sing this “new song,” we do not mean “new” in the sense that the song has just recently been written. The verse above refers to a song thousands of years old. Yet when sung by someone with a “clean heart” in whom the right spirit has been renewed, it is filled with new feeling and made into a new song. We sing to the Lord with hearts filled with love for Him who first loved us.