And they sung as it were a new song before the throne, and before the four beasts, and the elders: and no man could learn that song but the hundred and forty and four thousand, which were redeemed from the earth. They sung - a new song - See on Revelation 5:9 (note).
No man could learn that song - As none but genuine Christians can worship God acceptably, because they approach him through the only Mediator, so none can understand the deep things of God but such; nor can others know the cause why true believers exult so much in God through Christ, because they know not the communion which such hold with the Father and the Son through the Holy Ghost.