The appearance of a mighty angel indicates an important declarative action is to follow. A strong angel asked who was worthy to open the scroll (Rev. Rev. 5:2+). A mighty angel stood upon the sea and the land to proclaim the dominion of God in retaking the earth (Rev. Rev. 10:1+).
took up a great millstone and threw it into the sea
The angel now reenacts the declaration which Jeremiah told Seraiah to speak over the city thousands of years before:
So Jeremiah wrote in a book all the evil that would come upon Babylon, all these words that are written against Babylon. And Jeremiah said to Seraiah, When you arrive in Babylon and see it, and read all these words, then you shall say, O LORD, You have spoken against this place to cut it off, so that none shall remain in it, neither man nor beast, but it shall be desolate forever. Now it shall be, when you have finished reading this book, that you shall tie a stone to it and throw it out into the Euphrates. Then you shall say, Thus Babylon shall sink and not rise from the catastrophe that I will bring upon her. And they shall be weary. Thus far are the words of Jeremiah. (Jer. Jer. 51:60-64) [emphasis added]Jeremiahs declaration is another evidence which points to Babylon of the end being the literal city reconstructed on the banks of the Euphrates. For Seraiah was sent to the literal city in order to declare a literal judgment over her. The judgment he read has never been fulfilled in history (see Babylons Historic Fall). At the time of the end, the words of God regarding the city, as written by Jeremiah and declared by Seraiah, will find their ultimate fulfillment in the destruction of the rebuilt city of old. See Babylon is Babylon!.
Every word is employed to impress us with its suddenness and completeness. And inasmuch as all other fulfilled prophecies have been fulfilled to the very letter; and Babylon, though fallen gradually, and very low, has never suffered such a destruction. There is only one conclusion . . . it will be revived, and exceed all its former magnificence.1Jesus alluded to Jeremiahs predicted destruction of Babylon when he taught about the gravity of causing one of these little ones who believe in Me to sin (Mtt. Mat. 18:6; Mark Mark 9:42; Luke Luke 17:2).
Thus with violence
The angels actions demonstrate the severity and finality of Babylons destruction.
the great city
The angel parodies her boastful title when announcing her destruction. She considered herself great, nevertheless she will be completely overthrown. See commentary on Revelation 18:10.
shall not be found anymore
Shall not be found anymore is οὐ μὴ εὑρεθῆι ἔτι [ou mē heurethē eti] , no not it should be found still. The double-negative emphasizes her utter and permanent destruction. A similar prediction attended the destruction of Tyre (Eze. Eze. 26:18).