Late in his ministry, Jesus told parables about merchants, the first in Matthew (Matthew 25:14-30) and the second in Luke (Luke 19:12-27). In these stories the merchants were Jesus’ disciples who acted out of faith to gain other disciples for Jesus, thus, enlarging the Kingdom of God. The point is that “the merchants of the earth, (who) were waxed rich through the abundance of the great harlot’s delicacies” (Revelation 18:3), were the followers of the leadership of the Jerusalem’s authorities, who had rejected the Gospel by persecuting Jesus’ servants. These merchants were those who peddled Judaism around the world, and their works benefited from the adulterous acts of Jerusalem, the great harlot of the first century AD. In other words as the Jews looked to Caesar more and more (John 19:15), and the more they benefited in terms of wealth and prominence in Caesar’s world, the more Judaism was held in high esteem.
John heard yet another angel speak who had, presumably, been flying in the midst of heaven (cp. Revelation 14:6), and he commanded the Lord’s disciples to come out of Babylon (Revelation 18:4). Long ago, before there was a nation called Israel, Abraham, the father of that nation, pleaded with the Lord that he would not destroy the righteous with the unrighteous (Genesis 18:22-33), and the Lord answered his prayer (Genesis 19:12-22). Although there were many more than fifty righteous in Jerusalem and Judea in the first century AD, yet their numbers could not save the land of the Jews from destruction, due to the great unrighteousness of its people (cp. Ezekiel 14:12-14). Therefore, the Lord called out to the righteous, telling them to separate themselves from those evil men and not take part in their deeds (Revelation 18:4; cp. Numbers 16:26-27).
I find it interesting that the prophet, Jeremiah, spoke against Babylon (Jeremiah 51:12-14), describing her as a city that dwelt upon many waters (Jeremiah 51:13), meaning she was a city having great influence over nations and people of different languages (Revelation 17:1, 15, 18). Notice that Jeremiah also told the righteous to leave Babylon and deliver themselves from the Lord’s wrath (Jeremiah 50:8; 51:6, 45, 50), and he wasn’t the only prophet to make such a command (Isaiah 48:20; 52:11)! What is interesting is that the Jews, who were taken captive by Babylon, couldn’t simply leave and return to their homeland. They were powerless to carry out Jeremiah’s instructions, and neither could they simply leave after Babylon was captured by the Persians a few decades later. Cyrus had to make a decree permitting all who wished to return to their homeland to do so (Ezra 1:1-2). Nevertheless, the word of God cannot be broken (John 10:35). The Scriptures tell us that it was revealed to Jeremiah that he spoke not to the Jews of his generation, but rather to the righteous Jews of the first century AD (1Peter 1:10-12). It was those Jews who were commanded to leave Babylon and not take part in the judgment that would come upon her.
Another interesting thought that pertains to Jeremiah’s prophecy is what he commanded Seraiah, the quiet prince, to do (Jeremiah 51:59). Jeremiah prophesied in writing all that would come upon Babylon and commanded Seraiah to read that prophecy once he arrived in Babylon (Jeremiah 51:60-62). After he had obeyed Jeremiah’s command, Seraiah was to bind up the book with a stone and cast it into the Euphrates River, saying: “Thus shall Babylon sink and shall not rise from the evil that I will bring upon her…” (Jeremiah 51:63-64). If the great harlot, who sits upon many waters (Revelation 17:1), is that great city (Revelation 17:18), and, if those waters upon which she sits are nations and people of different languages (Revelation 17:15; cp. Jeremiah 51:63-64), and if her judgment was that a millstone would be wrapped around her and she was to be cast into the waters (the sea in the text), then it must be that Babylon (Jerusalem) would be destroyed, and she would be dispersed among the nations!
So, why would the Lord want to separate his elect from the rebels, whom he intended to judge? It is because judgment upon the rebels would be administered in such a way that it would be impossible to keep the elect from suffering the same fate as the evildoers, if they would remain with them (Revelation 18:4-5; cp. Genesis 18:22-33; 19:12-22)! Of course, some would conclude that nothing is impossible for God (Matthew 19:26; Mark 10:27), and that is correct. Nevertheless, escape or separation is the method the Lord intended to use to save the elect. To remain with the evildoers would have been foolish, if not disobedient (Psalm 50:18; Matthew 23:30; 1Timothy 5:22; 2John 1:11). Therefore, unless one wants to make God responsible for the fate of the disobedient or foolish, the only method of salvation out of the judgment and the wrath of God upon the rebels was for his elect to take flight (Matthew 24:15-22).
 See my studies: The Work of the Nobleman’s Servants for an understanding of how Jesus’ “merchants” should act, and The Work of the Wicked Servant for an idea of how Jesus’ “merchants” should not act.
 Jeremiah wrote his prophecy in the fourth year of the reign of Zedekiah, King of Judah. This was the same year that the king and all the people were carried off to Babylon (Jeremiah 51:59), so leaving Babylon (Jeremiah 51:45) was not an option at that time.