Chapter 18 announces the judgment. The one difficulty here is verse 4, coming where it is; but, as every difficulty in scripture, it leads into further light. The destruction of Babylon is simple enough. She falls by God's judgment just before Christ comes to judge the earth; and, first perhaps losing her power and influence, is destroyed by the horns and beast. The comparison of chapter 16:8, and the place it holds, chap. 16:19 , 18:8 , and the beginning of 19, make this plain. Chapter 18 is a warning from heaven, not the angel of judgment of the earth. It is not consequent on events, but supposes spiritual apprehension of heaven's mind. This is the case when it is simply a voice from heaven. This call then was a spiritual call, not a manifest judgment. It may be more urgent and direct just before judgment, and I doubt not will be: as the call is in Hebrews to come out of the camp because Jerusalem's day was at hand. Hence I believe this applies whenever we see the system to be Babylon, and the sense of her iniquities is pressed upon the conscience.
The chapter then goes on to the actual execution of judgment according to chapter 17:16. The horns, or kingdoms connected with the beast, have destroyed her. The kings mourn over her; so do those that have sought profit and ease and commerce in the earth. The royal and commercial system is shattered to pieces by the upset of the system. What characterises her, that for which she is judged, is idolatry, corruption, worldliness, and persecution. She is judged and destroyed, and the prosperity of the worldly is smitten by her fall, and the hopes of the kings who had commerce with her. The blood of all saints was found in her, as in Jerusalem in her day. Persecution comes from religion connected with worldly advantage. But what a picture we have here of the world, the relations of the kings and of the saints to Babylon!