This paragraph first describes a physical act John sees (Revelation 18:21). This action is followed by a verbal explanation of the significance of the physical act (Revelation 18:21–24). Within this verbal explanation there are three subsections: Revelation 18:21b relates what happens to Babylon; Revelation 18:22–23a relates what the result is; Revelation 18:23–24 provides three reasons why this happened to Babylon.
21 Then a mighty angel took up a stone like a great millstone and threw it into the sea, saying, “So will Babylon the great city be thrown down with violence, and will be found no more;