John Wesley on Revelation 5:9

And they sing a new song - One which neither they nor any other had sung before. Thou hast redeemed us - So the living creatures also were of the number of the redeemed. This does not so much refer to the act of redemption, which was long before, as to the fruit of it; and so more directly to those who had finished their course, "who were redeemed from the earth," Rev 14:1, out of every tribe, and tongue, and people, and nation - That is, out of all mankind.