John’s reference to “the beast and its image” directs the reader back to Revelation 13:14, where the beast from the earth had people construct an image for the first beast (of Revelation 13:1) so that by the pressure exerted by this beast and its image it might compel all people to worship it and slay those who resisted (Revelation 13:15).
2 And I saw what appeared to be a sea of glass mingled with fire and also those who had conquered the beast and its image and the number of its name, standing beside the sea of glass with harps of God in their hands.