New Defender's Study Bible Notes
15:1 another sign in heaven. This is the third great “sign” seen by John in heaven (see Revelation 12:1, 3), enabling him to look forward to the glorious future after the final series of judgments have cleansed the earth.
15:1 seven last plagues. Since this is specifically said to be a sign, the seven angels must be symbolic, representing all the angelic host, who eagerly anticipate the complete takeover of His inheritance by the Lamb, and who are thus ready to send the seven last plagues on the earth. Note that these are the last plagues, not just a parallel repetition of the seven seal judgments and the seven trumpet judgments. The seventh seal introduces the seven trumpets and the seventh trumpet encompasses the seven vials of wrath, with the seven last plagues.