Revelation 15:8

The smoke probably symbolizes the presence of God (cf. Exodus 19:18; Exodus 40:34; 1 Kings 8:10-11; 2 Chronicles 5:11-14; 2 Chronicles 7:1-3; Isaiah 6:4; Ezekiel 11:23; Ezekiel 44:4). No one could enter God’s presence until He had finished judging the earth-dwellers. This indicates the climactic nature of these judgments.

This chapter is really more of a prelude to chapter 16 than a conclusion to chapters 12-14. Chapters 12-14 record prophetically historical information about the Great Tribulation but not in the chronological sequence of the three sets of seven judgments (seals, trumpets, and bowls). Chapter 15 is similar to Revelation 8:1 in that it prepares for the next set of judgments, the bowls. It prepares for the resumption of the chronological progression of events on earth that ended temporarily in Revelation 11:19.