Chapters 17 and 18 are given to the apostle John outside the chronological flow of the 7 bowl judgments. They provide a flashback for orientation to "Babylon" which was judged at the 7th bowl.
The commentary by John Walvoord provides an accurate and valuable evaluation of both chapters.
I will stand on his shoulders and share his wisdom here so that on my site the reader can have access to it without having to look elsewhere.
Dr. Walvoord of course holds to the pretrib rapture position so I will make a few comments throughout in order to harmonize with the prewrath rapture position. But for the most part, the visions of chapter 17 and 18 have no direct bearing on the rapture positions.

18. The Fall Of Babylon

18:1-3 And after these things I saw another angel come down from heaven, having great power; and the earth was lightened with his glory. And he cried mightily with a strong voice, saying, Babylon the great is fallen, is fallen, and is become the habitation of devils, and the hold of every foul spirit, and a cage of every unclean and hateful bird. For all nations have drunk of the wine of the wrath of her fornication, and the kings of the earth have committed fornication with her, and the merchants of the earth are waxed rich through the abundance of her delicacies.

The opening phrase of chapter 18, “after these things,” marks a later revelation than that given in chapter 17. John declares, “I saw another angel come down from heaven.” The phrase “another angel” makes clear that the angel of chapter 18 is a different angel from that of 17:1. Though the angel is described as “having great power; and the earth was lightened with his glory,” it is evident that this is a literal angel and not a theophany, nor Christ in the form of an angel. The term “another” (Gr., allon) makes clear that this angel is the same in kind as the angel of 17:1. And the facts that the angel has great power and that the earth is lighted with the glory of the angel lead to the conclusion that the angel is delegated to do a great work on behalf of God. The announcement by the angel given in verses 2 and 3 declares that Babylon the great is fallen. The repetition of the verb “is fallen,” found in the aorist tense, indicates a sudden event viewed as completed, though the context would indicate a future event. Seiss believes that the repetition of the phrase “is fallen” is intended to describe two separate parts or stages of the fall, answering to the two aspects in which Babylon is contemplated, referring first to Babylon in mystery, as a system or spirit of false worship, and second to Babylon as a city, in which this system or spirit is finally embodied.²⁸⁷

The announcement of chapter 18 coming so closely after the destruction of the harlot in chapter 17 has, however, raised a question as to whether the two are one and the same event.

There are a number of reasons for believing that chapter 18 is a subsequent event, though described in similar terms. The woman who is destroyed in chapter 17 is made desolate, naked, and burned with fire by the beast with the ten horns. From this it may be concluded that the destruction of the harlot in chapter 17 is the fall of Babylon in its ecclesiastical or religious sense and that it probably occurs when the beast assumes the role of God at the beginning of the great tribulation. The world church is destroyed in favor of a world religion honoring the political dictator, the beast out of the sea of chapter 13.

In chapter 18, the context seems to indicate that Babylon here is viewed in its political and economic character rather than in its religious aspect. The term “Babylon” in Scripture is more than a reference to the false religious system which stemmed from the false religion of ancient Babylon. Out of ancient Babylon also came the political power represented in Nebuchadnezzar and fulfilled in the first world empire. In some sense this is continued in the commercial system which came from both the religious and the political Babylons. It seems that chapter 17 deals with the religious aspect and chapter 18 with the political and economic aspects of Babylon.

According to verse 9 the kings of the earth as well as the merchants will mourn the passing of the Babylon of chapter 18. There is apparently no mourning connected with the destruction of the woman in chapter 17. The destruction of Babylon in chapter 18 should be compared with the preceding announcement in 16:19 where the great city is divided and the cities of the Gentiles fall. This event comes late in the great tribulation, just prior to the second coming of Christ, in contrast to the destruction of the harlot of chapter 17 which seems to precede the great tribulation and paves the way for the worship of the beast (13:8).
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Of course, by the term "second coming" Dr. Walvoord is referring to  Revelation 19:11ff. According to the prewrath view of the rapture, the second coming is when Jesus arrives in the clouds of the sky with power and great glory at an unknown day and hour after a divine decree amputates or cuts short the great tribulation. Jesus remains ON the cloud until Revelation 19 when at that time He will descend physically onto the earth to confront the nations in the Armageddon campaign. So according to prewrath, the descent at Armageddon is NOT the second coming.
I believe that Rev. 19:11-16 describes that second coming that will occur at the 6th seal. The vision shown to John then skips over all the many events that follow that second coming (the day of the Lord judgments through the trumpets and bowls) and jumps right to the final battle at Armageddon. This is not uncommon for the prophets. They often stated the arrival of the Messiah (the day of the Lord) and then skipped over many events to focus on one particular one - quite often the battle of Armageddon.
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The downfall of the city of Babylon in 18:2 is followed by its becoming the habitation of demons, the “hold” or “prison” of every evil spirit, and the “cage,” the same word in the Greek as “hold” (phylake), of every unclean and hateful bird. The threefold description of the inhabitants of fallen Babylon is a reference to fallen angels in their various characteristics as demons and evil spirits, symbolized by the bird (cf. “birds,” Isa. 34:11-15; Matt. 13:32). This abandonment of destroyed Babylon to demons is a divine judgment stemming from the utter wickedness of its inhabitants described in verse 3. Babylon in her political character has had evil relationships with “all nations” described as “fornication.” In this, they have been led by the rulers, “the kings of the earth.” The resulting evil association has made the merchants of the earth rich. Just as the church had grown rich in proportion as it had been wicked, so the nations have likewise prospered, as they have abandoned God and sought to accumulate wealth of this world. The wealth originally collected through the influence of the apostate church is taken over by the political system in the great tribulation which with universal political power is able to exploit to the full its accumulation of wealth.

18:4-5 And I heard another voice from heaven, saying, Come out of her, my people, that ye be not partakers of her sins, and that ye receive not of her plagues. For her sins have reached unto heaven, and God hath remembered her iniquities.

As John contemplates the announcement of the fall of Babylon, he hears another voice from heaven addressed to the people of God instructing them to come out of Babylon. In a similar way the people of God were urged to leave Babylon in ancient days (Jer. 51:45). Seiss explains the phrase “come out of her,” citing Jeremiah 50:4-9 where the children of Israel are urged to “remove out of the midst of Babylon” (Jer. 50:8), and the command “Flee out of the midst of Babylon, and deliver every man his soul” (Jer. 51:6).²⁸⁸ Alford compares the command to come out of Babylon to the warning to Lot to leave Sodom (Gen. 19:15-22).²⁸⁹ The purpose of leaving Babylon is twofold: first, by separation from her they will not partake of her sin, and second, they will not have her plagues inflicted on them. The reference to plagues refers to the vials of chapter 16, especially the seventh vial which falls upon Babylon itself (16:17-21). This is further evidence that the event of chapter 18 is subsequent to the seventh vial and therefore in contrast to the destruction of the harlot in chapter 17.

In verse 5 the sins of Babylon are declared to reach to the heavens with the result that God remembers, that is, judges her iniquities (cf. Jer. 51:9). The fact that her sins have reached (Gr., kollao, literally “glued” or “welded together,” i.e., piled one on another as bricks in a building) unto heaven is an allusion to the tower of Babel which began the wicked career of ancient Babylon (Gen. 11:5-9). Though God perm/its the increment of sin, its ultimate divine judgment is inescapable.

18:6-8 Reward her even as she rewarded you, and double unto her double according to her works: in the cup which she hath filled fill to her double. How much she hath glorified herself, and lived deliriously, so much torment and sorrow give her: for she saith in her heart, I sit a queen, and am no widow, and shall see no sorrow. Therefore shall her plagues come in one day, death, and mourning, and famine; and she shall be utterly burned with fire: for strong is the Lord God who judgeth her.

In keeping with the enormity of her sin, the voice from heaven now calls on God to reward Babylon even as she rewarded the people of God. The verb (Gr., apodidomi) means literally “to pay a debt” or “to give back that which is due.” It is the law of retribution sometimes called lex talionis. Divine justice exacts the “eye for an eye” and the “tooth for a tooth.”

The normal law of retribution, however, is here doubled in recognition of the enormity of the sin of Babylon. Accordingly the voice demands, “Double unto her double according to her works.” In keeping with this principle, the cup of iniquity which Babylon filled is now to be filled twice with the measure of her judgment. There is no mercy for the utter apostasy found in Babylon in all her phases of operation. The verb (Gr., kerannymi) translated “fill” is literally “mix” or “mingle” as in the preparation of a drink. The same verb is used in 14:10 in connection with the wine of the wrath of God.

The same law of retribution is indicated in verse 7 where the standard of her judgment is compared to her luxurious living in which she was given to self-glorification. The expression “lived deliciously” (Gr., estre-niasen) means “to be wanton” or “to revel” and comes from a word meaning “hardheaded” or “strong.” Her willful sin against God is now to be rewarded with torment and sorrow. The “torment” (Gr., basanismon) refers to trial by torture with its resultant mental anguish and grief (Gr., penthos). Her wishful thinking in which she said, “I sit a queen, and am no widow, and shall see no sorrow” is going to be rewarded by sudden destruction from the Lord which according to verse 8 will come in one day in the form of plagues, death, mourning, and famine, resulting in her utter destruction by fire. Her vaunted strength is as nothing compared to the power of God. Like the church at Laodicea, her wealth has brought a sense of false security (3:17). Her claim to not being a widow has only the faulty foundation of her illicit love affairs with the kings of the earth (17:2). The fact that her judgment comes in one day, emphasized in the Greek by being placed first in the sentence, is reminiscent of the fall of Babylon in Daniel 5, which fell in the same hour that the finger traced its condemning words upon the wall. Before morning, the ancient power of Babylon has been destroyed. In a similar way, the rich fool of Luke 12:16-20 lost his barns and his soul in one night. When it is time for God’s judgment, it descends with unwavering directness.

18:9-10 And the kings of the earth, who have committed fornication and lived deliciously with her, shall bewail her, and lament for her, when they shall see the smoke of her burning, Standing afar off for the fear of her torment, saying, Alas, alas, that great city Babylon, that mighty city! for in one hour is thy judgment come.

The destruction of Babylon in its political and economic aspects described in the preceding verses is now the subject of a lament by the kings of the earth. These kings are a wider designation than the ten kings of 17:12,16, who participated in the destruction of the harlot. Here there is lament over the destruction of that which remained. The time is the second coming of Christ at the end of the great tribulation. The very kings who participated in the wickedness and wealth of Babylon now mourn her passing, symbolized in the burning of the capital city. The lament of the kings over Babylon is most emphatic in the Greek by the repetition of the article: literally “the city the great, Babylon the city the mighty.” It was great in its extent of power and accomplishment and mighty in the strength of its rule. In spite of its greatness and strength (Gr., megale and ischyra), it nevertheless falls in one hour.
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Again, for the sake of consistency, I need to point out that the second coming that Walvoord refers to occurs at Rev. 19:11-16. And while this is indeed a summary statement of the arrival of Jesus as is symbolized at the 6th seal of Rev. 6, he sees it as occurring at the end of the 70th week. Then what John is shown is the assembly of armies at Armageddon which will occur several months after the arrival at verse 11.
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Some believe that ancient Babylon is to be rebuilt as the capital of the world empire in the great tribulation period and that Babylon in this chapter refers to ancient Babylon rather than to Rome. According to Isaiah 13:19-22, Babylon was to be completely destroyed and not inhabited. This seems also the teaching of Jeremiah 51:24-26, 61-64. It is argued that ancient Babylon as a city was not destroyed for hundreds of years after the fall of the empire and therefore these prophecies have not been literally fulfilled.

The destruction of Babylon according to Jeremiah 51:8 was to be sudden. This is confirmed by Revelation 18:17-19. As far as the physical city of Babylon was concerned, this was not true of ancient Babylon as it continued for many years after its political downfall. Further, it is pointed out that the prophecy of Isaiah 13:6, &-11, which formed the context of Isaiah 13:19-22, indicates that the destruction of Babylon would be in the day of the Lord.²⁹⁰ Hence, it is held that Babylon will be rebuilt and then destroyed by Christ at His second coming.

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Actually, this statement is not incorrect as long as we realize that the destruction will not occur immediately at the second coming of Christ (ACTUAL), but later during the Armageddon campaign.
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Others identify Babylon as Rome, the seat of the apostate church as described by the seven mountains of 17:9 and also the political city as elsewhere described.²⁹¹ It is possible that Rome might be the ecclesiastical capital and rebuilt Babylon the political and commercial capital. It is also conceivable that Rome might be the capital in the first half of the last seven years and Babylon in the second half—in the world empire phase. Haldeman holds that Babylon will be rebuilt. He states, “Rome will be the political, Babylon the commercial, capital of Antichrist’s kingdom.”²⁹² On the other hand Hoste observes, “I do not think there is any necessity that Babylon should be rebuilt, for another city has, as we see in this chapter, taken her place.”²⁹³

Those who deny that Babylon will be rebuilt do so on the principle that the prophecy of destruction refers to ecclesiastical and political power symbolized in Babylon but not embodied in an actual city. The city of Babylon politically therefore is now destroyed historically. The power and religious character of Babylon are destroyed at the second coming. The ultimate decision depends upon the judgment of the expositor, but in many respects it is simpler to postulate a rebuilt Babylon as fulfilling literally the Old Testament prophecies as well as that embodied in this chapter.

Regardless of location, the burning of the city is a symbol of the fall of its political and economic might, and the kings of the earth marvel at the destruction of the seemingly infinite power of the capital of the world empire. The twofold lament involved in the words bewail and lament indicates to vocally lament (bewail) and to beat the breast (lament, Gr., kopsontai). Their vocal lament, “Alas, alas” (Gr., ouai) is probably better translated “Woe, woe” because it is much more emphatic than the English “alas.” The word is mournful in both its sound and meaning and is reminiscent of the hopeless wailing of those who mourn the passing of loved ones. Their mourning is also characterized by fear lest they have the same judgment which has overcome the city, and for this reason they stand afar off. How sad is the hour of judgment when it is too late for mercy.

18:11-19 And the merchants of the earth shall weep and mourn over her; for no man buyeth their merchandise any more: The merchandise of gold, and silver, and precious stones, and of pearls, and fine linen, and purple, and silk, and scarlet, and all thyme wood, and all manner vessels of ivory, and all manner vessels of most precious wood, and of brass, and iron, and marble, And cinnamon, and odours, and ointments, and frankincense, and wine, and oil, and fine flour, and wheat, and beasts, and sheep, and horses, and chariots, and slaves, and souls of men. And the fruits that thy soul lusted after are departed from thee, and all things which were dainty and goodly are departed from thee, and thou shalt find them no more at all. The merchants of these things, which were made rich by her, shall stand afar off for the fear of her torment, weeping and wailing, And saying, Alas, alas that great city, that was clothed in fine linen, and purple, and scarlet, and decked with gold, and precious stones, and pearls! For in one hour so great riches is come to nought. And every shipmaster, and all the company in ships, and sailors, and as many as trade by sea, stood afar off, And cried when they saw the smoke of her burning, saying, What city is like unto this great city! And they cast dust on their heads, and cried, weeping and wailing, saying, Alas, alas that great city, wherein were made rich all that had snips in the sea by reason of her costliness! for in one hour is she made desolate.

The economic character of the city of Babylon is indicated in the fact that the merchants also weep and mourn for her. Their grief is occasioned by the loss of their trade with the city. The rich and varied character of the merchandise is itemized in verses 12 and 13, beginning with precious stones and costly metals characteristic of wealth and luxury. Next in order are the fine fabrics used in their clothing, composed of fine linen and silk in the luxurious colors of purple and scarlet. Precious stones, versatile metals, and fine fabrics which constituted the wealth of the ancient world are here itemized as the treasure of Babylon in the hour of her destruction. The luxury of their apparel is matched by the rich furnishings of their homes including articles of thyine and other precious wood, ivory, brass, iron, and marble. Thyine was a fragrant wood corresponding to cypress and was used for expensive furniture in Roman times along with other precious materials. The use of vessels made of ivory, brass, iron, and marble as well as precious wood was symbolic of the luxury and wealth of Babylon before its destruction.

In verse 13 expensive perfumes and spices are mentioned, such as cinnamon, unspecified odors (Gr., amomon, from an odiferous shrub of which an ointment was made, translated “spice” in the A.R.V.), and ointments (Gr., myron, an unguent made of an aromatic juice). Some manuscripts add “incense” between “odours” and “ointments” (Gr., thymiamata). The last luxury item to be listed is frankincense. All of these could be afforded only by the wealthy. Next is mentioned the abundance of foods, such as wine, oil, fine flour, wheat, cattle, and sheep. The word beasts (Gr., ktene„), used as a general word for property in the form of animals, probably refers to cattle. Verse 13 closes with reference to the means of transportation employed by the wealthy, namely, horses and chariots, and finally, the slaves they possessed in body and soul. The combined picture is one of complete abandonment to the wealth of this world and total disregard of God who gave it.

Verse 14 tells of the sweeping removal of all these precious possessions described as “the fruits that thy soul lusted after” and “all things which were dainty and goodly.” The inhabitants of Babylon addressed as “thou” are no longer able to find these things. Like the kings of the earth who stood afar off and watched the ascending smoke of the burning of Babylon, so the merchants also shall fear to go near the city. Weeping and wailing, that is, crying out loud and mourning, they also repeat their sad “alas” (Gr., ouai). All the great riches of the city, described again as fine linen, purple and scarlet, gold, precious stones, and pearls, are brought to nothing.

Those in ships, apparently standing off from shore on the sea, witness the scene and join in the mourning as they see the smoke of the city ascending. They cry saying, “What city is like unto this great city!” In expression of their grief, they cast dust on their heads and join other merchants in weeping and wailing. For the third time in the passage, the mourning cry “Ouai ouai” is heard. Their mourning is not for the city, however, but because their wealth derived from trade in shipping is now at an end. Christ warned against coveting the wealth of this world when He said,

Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal: But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal: For where your treasure is, there will your heart be also (Matt. 6:19-21).

In contrast to the transitory wealth and glory of this world, which are here consumed by a great judgment from God, are the true riches of faith, devotion, and service for God laid up in heaven beyond the destructive hands of man and protected by the righteous power of God. The destruction of Babylon also ends the nefarious control of the souls of men mentioned last in the list of commodities in verse 13. No longer can ancient Babylon control the world religiously, politically, or economically.

18:20 Rejoice over her, thou heaven, and ye holy apostles and prophets; for God hath avenged you on her.

In contrast to the grief overtaking worldly rulers and merchants by the destruction of Babylon, those in heaven, who are mentioned later in 19:1, are called upon to rejoice at the righteous judgment of God. The address is to “the saints and the apostles and the prophets” rather than to the “holy apostles,” with the article repeated each time. The expression “hath avenged” is literally “God hath judged your judgment on them,” that is, “God hath inflicted your judgment on them,” thus bringing to bear upon Babylon the righteous recompense for her martyrdom of the saints. It is another case where the righteous ultimately triumph as victory follows suffering.

18:21-24 And a mighty angel took up a stone like a great millstone, and cast it into the sea, saying. Thus with violence shall that great city Babylon be thrown down, and shall be found no more at all. And the voice of harpers, and musicians, and of pipers, and trumpeters, shall be heard no more at all in thee; and no craftsman, of whatsoever craft he be, shall be found any more in thee; and the sound of a millstone shall be heard no more at all in thee; And the light of a candle shall shine no more at all in thee; and the voice of the bridegroom and of the bride shall be heard no more at all in thee: for thy merchants were the great men of the earth; for by thy sorceries were all nations deceived. And in her was found the blood of prophets, and of saints, and of all that were slain upon the earth.

John in his vision now sees a “mighty angel” (cf. 5:2; 10:1) throw a stone like a great millstone into the sea, portraying the violent downfall of the great city. A similar instance is found in Jeremiah 51:61-64. In this passage in Jeremiah, Seraiah, a prince who accompanied Zedekiah into Babylon, is instructed after reading the book of Jeremiah to bind a stone to it and cast it into the midst of the Euphrates with the words “Thus shall Babylon sink, and shall not rise from the evil that I will bring upon her: and they shall be weary.” In the similar instance portrayed in Revelation, the millstone is cast into the sea instead of the Euphrates. The symbolism is the same. It represents the destruction of the great city, which like a stone cast into the sea will be found no more. The ultimate end of Babylon in all its forms will be accomplished by God’s judgment at the end of the great tribulation. Babylon will be found “no more at all” (cf. vv. 14, 22-23). The expression occurs seven times with minor variations.

The angel now enlarges on the cessation of activity in this great city. That which characterized its life and featured its luxurious existence, such as the voices of harpers and musicians, of pipers and trumpeters, who added to the fanfare and public display of both the religious and political Babylon, is now silent. Similarly, the fine craftsmen who produced the ultimate in luxurious goods are no longer to be found. The sound of the millstone grinding out the grain is silent. In like manner, the light of the candle is now out, the city cold and dead, and no longer do its streets ring with the voices of the bridegroom and the bride. Of the nine different features mentioned, seven are described as “the voice” (Gr., phone„, literally “sound”) of harpers, musicians, pipers, trumpeters, millstone (“sound” same as “voice” in Greek), bridegroom, and bride. The very silence of the city is a testimony to God’s devastating judgment.

Verses 23 and 24 provide another brief summary of the extent of Babylon’s sins and greatness. Her merchants were “great men of the earth.” All nations were deceived by Babylon’s sorceries. Here too was the martyred blood of prophets and saints. The greatness that was the secret of her rise in power and influence makes her downfall all the more impressive. Babylon is declared to be guilty of the blood of prophets and saints, reference in part to the martyrs of the great tribulation.

There is an obvious parallel in the rise and fall of Babylon in its varied forms in Scripture. As introduced in Genesis 11:1-9, Babylon, historically symbolized by the tower reaching to heaven, proposed to maintain the union of the world through a common worship and a common tongue. God defeated this purpose by confusing the language and scattering the people. Babylon, ecclesiastically symbolized by the woman in Revelation 17, proposes a common worship and a common religion through uniting in a world church. This is destroyed by the beast in Revelation 17:16 who thus fulfills the will of God (Rev. 17:17). Babylon, politically symbolized by the great city of Revelation 18, attempts to achieve its domination of the world by a world common market and a world government. These are destroyed by Christ at His second coming (Rev. 19:11-21). The triumph of God is therefore witnessed historically in the scattering of the people and the unfinished tower of Genesis 11 and prophetically in the destruction of the world church by the killing of die harlot of Revelation 17 and in the destruction of the city of Revelation 18. With the graphic description of the fall of Babylon contained in chapters 17 and 18, the way is cleared for the presentation of the major theme of the book of Revelation, the second coming of Christ and the establishment of His glorious kingdom.
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²⁸⁷ Joseph A. Seiss, The Apocalypse, p. 407.

²⁸⁸ Ibid., p. 408.

²⁸⁹ Henry Alford, The Greek New Testament, IV, 715.

²⁹⁰ See the extended discussion presenting evidence for the futurity of the final judgments on Babylon in B. W. Newton, Babylon and Egypt, Their Future History and Doom, pp. 1-30.

²⁹¹ Cf. previous discussion of Rev. 17:9-11; also cf. Seiss, pp. 397-415.

²⁹² I. M. Haldeman, A Synopsis of the Book of Revelation, p. 21.

²⁹³ William Hoste, The Visions of John the Divine, p. 129.