(9) And they sung a new song, saying, Thou art worthy to take the book, and to open the seals thereof: for thou wast slain, and hast redeemed us to God by thy blood out of every kindred, and tongue, and people, and nation;
(10) And hast made us unto our God kings and priests: and we shall reign on the earth.
“A new song” is sung by the twenty-four elders (the New Testament priests). The concept of singing a new song is not foreign to scripture (Psalm 33:3, 40:3, 96:1, 98:1, 144:9, 149:1, and Isaiah 42:10). As it can be seen in from those scriptures, a new song is always sung fresh out of deliverance, redemption, and salvation. It is a new day and a new song. Yesterday was dark and dreadful; today the sun is shining bright. Yesterday’s song was for deliverance and help; today’s song different, new, and filled with praise for the Lord has brought deliverance.
The rest of verses nine and ten relate to the identity of the twenty-four elders, who have described as: 1) Redeemed by the blood of the lamb; 2) People from every nation and language under heaven; 3) Kings; 4) Priests. These descriptions can only refer to New Testament saints because the priesthood in the Old Testament was limited to the family of Aaron of the tribe of Levi; and the Old Testament kings were limited to Judah. The people described here are priests and kings (not possible to be from Levi and from Judah), and they are from every nation and language under heaven. This can only be a reference to the saints under the New Covenant. For a full discussion of the identity of the twenty-four elders, see comments on 4:4).