And again they said, Alleluia - See the notes on Revelation 19:1. The event was so glorious and so important; the final destruction of the great enemy of the church was of so much moment in its bearing on the welfare of the world, as to call forth repeated expressions of praise.
And her smoke rose up forever and ever - See the notes on Revelation 14:11. This is an image of final ruin; the image being derived probably from the description in Genesis of the smoke that ascended from the cities of the plain, Genesis 19:28. On the joy expressed here in her destruction, compare the notes on Revelation 18:20.

Her smoke rose up - There was, and shall be, a continual evidence of God's judgments executed on this great whore or idolatrous city; nor shall it ever be restored.

And again they said, (3) Alleluia. And her smoke rose up for ever and ever.
(3) The song of the Antiphony or response, containing an amplification of the praise of God, from the continuous and certain testimony of his divine judgment as was done at Sodom and Gomorrah, (Genesis. 19:1-38).

And again they said, Alleluia,.... Or a "second time" they said it; they began and ended their solemn worship and service with it; so some psalms begin and end with this word, translated in the Old Testament by the words "Praise ye the LORD", as in Psalm 106:1 &c. and the repeating of the word shows how hearty, arnest, and constant they were in the work of praise on this account:
and her smoke rose up for ever and ever; they repeated their hallelujah, or gave one spiritual "huzza" more at the burning of Rome, and this followed: or the words may be rendered, "for her smoke rose", &c. and so are a reason for the second "hallelujah": it looks as if Rome, like another Sodom and Gomorrah, would sink into a sulphurous burning lake, and continue so: respect is had to the everlasting punishment of antichrist and his followers in hell, and to the everlasting burnings that will follow Rome's temporal destruction, which was an example and symbol of the vengeance of eternal fire; see Revelation 14:11 so the Jews (o) say of the burning of Rome, that its fire shall not be quenched for ever, and that "its smoke shall rise up for".
(o) Yalkut Simeoni, par. 2. fol. 48. 2.

again--Greek, "a second time."
rose up--Greek, "goeth up."
for ever and ever--Greek, "to the ages of the ages."