Revelation 18:15-20
(Rev 18:15 KJV)
The merchants of these things, which were made rich by her, shall stand afar off for the fear of her torment, weeping and wailing,

The merchants who lived and received their luxuries from Babylon are now standing afar off because of the torment that Babylon is now receiving. They, like the kings of the earth, are weeping and wailing because of the destruction which has come upon the object of their life’s desires. Now as they watch the destruction of Babylon, they know that because of their agreement with the beast system and their rejection of God that judgment is coming upon them also.

(Rev 18:16 KJV)
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!

The merchants who thought that their wealth would continue unabated had neglected to take into consideration the fact that it is God who owns this world and not the corporate executive or the banker.
(Psa 24:1 KJV) The earth is the LORD'S, and the fulness thereof; the world, and they that dwell therein. Now the time has come to purify the earth with fire and remake it new in righteousness. The great abundance of riches and wealth which the Lord placed on this earth became a snare to the unbeliever who worked their whole life to gain as much as they can. What was once a great and wealthy world was now going to be consumed in the flames and that is why those who trust in riches are wailing. (1 Tim 6:17 KJV) Charge them that are rich in this world, that they be not highminded, nor trust in uncertain riches, but in the living God, who giveth us richly all things to enjoy; Paul had urged Timothy to warn those that have much earthly goods that there is no way they are going to keep them one minute past their death. This is why the Bible calls riches uncertain because one day you may have them and the next day you will not.

(Rev 18:17 KJV)
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,

Here is the third group which is making lamentation over Babylon. It is those who are the ship masters plus all the sailors. The sailors would represent all the unbelievers of the world who do not hold any exalted positions as kings, merchants, or shipmasters. Now all the unbelievers in the world are weeping and wailing as they too watch the destruction of Babylon from the judgment throne of Christ. Every unbeliever had placed their trust in the world system and now they too are seeing that they have been deluded and the day of their judgment has come also. The sea represents the world as we have previously seen.
(Isa 17:12-13 KJV) Woe to the multitude of many people, which make a noise like the noise of the seas; and to the rushing of nations, that make a rushing like the rushing of mighty waters! {13} The nations shall rush like the rushing of many waters: but God shall rebuke them, and they shall flee far off, and shall be chased as the chaff of the mountains before the wind, and like a rolling thing before the whirlwind. Any unbeliever, regardless of social rank who has placed their trust in the world system or followed its pernicious ways will suffer the eternal consequences which the beast will also suffer.

(Rev 18:18 KJV)
And cried when they saw the smoke of her burning, saying, What city is like unto this great city!

As Ezekiel reports, the city of Tyre is going to face a similar judgment when it finally falls at the hand of God’s judgment.

(Ezek 27:27 KJV) Thy riches, and thy fairs, thy merchandise, thy mariners, and thy pilots, thy calkers, and the occupiers of thy merchandise, and all thy men of war, that are in thee, and in all thy company which is in the midst of thee, shall fall into the midst of the seas in the day of thy ruin.

Then the people are going to take up a lament concerning the city of Tyre.

(Ezek 27:32 KJV) And in their wailing they shall take up a lamentation for thee, and lament over thee, saying, What city is like Tyrus, like the destroyed in the midst of the sea?

Those who took up a lamentation for the city of Tyre had asked, “what city is like Tyre?” Well those who will be weeping over Babylon will say the same thing because they thought that Babylon was invincible the same way those who lived in Tyre thought their city was invincible and impervious to judgment. Babylon was a great city and held her people in awe with her strength but now the day of reckoning has come and those who trusted in Babylon for their security now wail and lament as they see their earthly god burning in judgment.

(Rev 18:19 KJV)
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 ships in the sea by reason of her costliness! for in one hour is she made desolate.

These people are not casting dust on their heads in repentance because the day of salvation is now over. They are casting dust on their heads in response to the judgment which has come upon Babylon and which is now coming upon them. Here we are told in one hour she is made desolate which means that God is repeating here that the judgment of Babylon is going to be swift and complete. Even in their lamenting, the thing that is on their mind is the riches they knew when they were living in accord with Babylon. The absence of repentance and the absence of calling upon God is very noticeable here. The unbeliever still lusts after the riches of the earth even while they are facing eternal judgment.
(Rev 22:11 KJV) He that is unjust, let him be unjust still: and he which is filthy, let him be filthy still: and he that is righteous, let him be righteous still: and he that is holy, let him be holy still. Revelation 22:11 teaches us that the unbeliever will still remain in unbelief and the believer will remain in belief. This is why the merchants last thought is of riches. When Israel came out of Egypt, their thoughts went to the good food they had to eat but they quickly forgot that they were fed well because they were slaves and had to work many hours each day. Unbelievers are tied only to the sensual delights of this world.

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

(Rom 12:19 KJV) Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord.

(2 Th 1:8 KJV) In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ:

Injected into the final judgment upon Babylon is this command to rejoice over its destruction. The word “rejoice" is in the imperative mood which makes it a command. God is commanding all His children to rejoice that the kingdom of evil has now been judged and has been destroyed. This may sound a bit harsh but think of all the evil which Babylon had brought upon the true believer throughout history.
(Jer 11:14 KJV) Therefore pray not thou for this people, neither lift up a cry or prayer for them: for I will not hear them in the time that they cry unto me for their trouble.  In the Jeremiah verse God is telling Jeremiah not to pray for the people of Judah because they have sinned so greatly that God will not hear their voice. The same principle is found in 18:20 where the people of God are not to be remorseful over the doom of the kingdom of evil which was the archenemy of the kingdom of God.