The song begins with a declaration of the Lamb’s worthiness to take the scroll and open its seals. With those words the song recounts the newest development in redemptive history. The song then recounts three reasons why the Lamb was worthy.
The Lamb was slain (Revelation 5:6). That’s a reference to his work on the cross of Calvary where he laid down his life in place of those deserving to die (fulfilling OT sacrifices).
By his blood he ransomed people for God. By these words the elders acknowledge that the Lamb’s sacrifice on the cross had blessed results.
The ransomed have been formed into a kingdom and priests to God (Revelation 5:10).
9 And they sang a new song, saying, “Worthy are you to take the scroll and to open its seals, for you were slain, and by your blood you ransomed people for God from every tribe and language and people and nation,