What does Revelation 18:4 mean?

Apparently, saved Jews and Gentiles will live and work in Babylon and other major cities. This would not be without difficulty, given restrictions imposed by the False Prophet (Revelation 13:16–17). The apostle John heard a voice from heaven summoning believers to exit Babylon. There was the danger of becoming part of the problem instead of part of the solution. If the believers stayed in Babylon, they might succumb to the temptation to partake of its cultural and religious life.

Genesis 13 relates the story of Lot separating himself from his uncle, Abraham, and settling near Sodom. He did this despite the city's reputation for immorality (Genesis 13:13). Eventually, Lot became so complacent that he moved into Sodom. Just before God destroyed the city, two angels urged Lot to evacuate. When he lingered, they physically dragged him and his family out of the city (Genesis 19:1–22). Obviously, he and his wife and two daughters had found Sodom somewhat attractive. Nevertheless, the attraction ended for Lot when the Lord turned the city, all its residents, and contents into heaps of ashes (Genesis 19:23–29).

God has never commanded His people to be a part of the evil world system. His command is to be apart from the evil world system. Living "in" a fallen world does not mean living "like" those who are unbelievers (1 Corinthians 5:9–11). Second Corinthians 6:14 asks: "What partnership has righteousness with lawlessness? Or what fellowship has light with darkness?" Sharing the sins of the evil world system, or being in close contact with it, leads to the tragedy of sharing its judgment.