Albert Barnes on Revelation 15:1

And I saw another sign in heaven. Another wonder or extraordinary symbol. The word sign here--σημειον--is the same which in Rev 12:1,3, 13:13, is rendered wonder and wonders, and in Rev 13:14, 16:14, 19:20, miracles. The word is not elsewhere found in the book of Revelation, though it is of frequent occurrence in other parts of the New Testament. See it explained in Barnes on "Re 12:1". Here it is used to denote something wonderful or marvellous. This is represented as appearing in heaven, for the judgments that were to fall upon the world were to come thence. Compare Rev 11:19, Rev 12:1, 14:1,6,13-14,17.

Great and marvellous. Great and wonderful, or fitted to excite admiration--θαυμαστον. The subsequent statements fully justify this, and show that the vision was one of portentous character, and that was fitted to hold the mind in astonishment.

Seven angels. Compare Barnes on "Re 1:4".

Having the seven last plagues. The article here, "the seven last plagues," would seem to imply that the plagues referred to had been before specified, or that it would be at once understood what is referred to. These plagues, however, have not been mentioned before, and the reason why the article is used here seems to be this: the destruction of this great Antichristian power had been distinctly mentioned, Revelation 14. That might be spoken of as a thing now well known, and the mention of it would demand the article; and as that was well known, and would demand the article, so any allusion to it, or description of it, might be spoken of in the same manner, as a thing that was definite and fixed, and hence the mention of the plagues by which it was to be accomplished would be referred to in the same manner. The word plagues--πληγας, from πληγη--means properly a wound caused by a stripe or blow, and is frequently rendered stripe and stripes, Lk 12:48, Acts 16:23,33, 2Cor 6:5, 11:23. It does not elsewhere occur in the New Testament except in the book of Revelation. In this book it is rendered wound in Rev 13:3,12,14; and plagues in Rev 9:20, 11:6, 15:1,6,8, 16:9,21, 18:4,8, 21:9, 22:18. It does not occur elsewhere. The secondary meaning of the word, and the meaning in the passage before us, is a stripe or blow inflicted by God; calamity or punishment. The word "last" means those under which the order of things here referred to would terminate; the winding up of the affairs respecting the beast and his image--not necessarily the closing of the affairs of the world. Important events were to occur subsequent to the destruction of this Antichristian power, (Chapters 19-22) but these were the plagues which would come finally upon the beast and his image, and which would terminate the existence of this formidable enemy.

For in them is filled up the wrath of God. That is, in regard to the beast and his image. All the expressions of the Divine indignation towards that oppressive and persecuting power will be completed or exhausted by the pouring out of the contents of these vials. Compare Barnes on "Re 10:7", where the word rendered filled up-- ετελεσθη--is rendered finished.

(g) "wrath" Rev 14:10