The opening description of Babylon in Revelation 18 suggests a city depopulated and repopulated. The people have been moved out, and in their place it has been infested with impurity. There are four categories of new inhabitants: demons and unclean spirits, unclean and abominable birds, and they are divided into three groups by three terms for their location: Demons are in the “habitation,” there is a “prison” for unclean spirits, and another “prison” for unclean and detestable birds. The Greek clause has twelve words.
The description alludes to Old Testament passages that describe fallen cities as habitations of birds. Isaiah 13:21-22 emphasizes that the city that is described as being overthrown like Sodom and Gomorrah becomes a habitation for desert creatures, for owls and ostriches, wild goats, hyenas and jackals. The city is the high point of human culture; it is a garden glorified. Isaiah warns that the city-garden will become desolate, that is, it will suffer desertification (cf. also Isaiah 34:11-15; Jeremiah 50:39; 51:37; Zephaniah 2:14). Human beings control and rule animals. When human beings depart, the animals take over. When good human beings leave, bestial and demonic people take over.
At the same time that the birds and demons are moving in, the people of God are exhorted to leave. This is an exodus scene, a return from Babylonian exile. As Egypt was collapsing, and as the Amalekites moved on, Israel was on its way to the promised land. When Babylon was overthrown and the Persians moved in, Israel was released from the bondage of exile. Here, Babylon is old Jerusalem, and as she collapses, drunk with the blood of the saints, and is infested with demons, a voice from heaven calls on Israel to leave.
Jesus had the same message in His Olivet Discourse: When you see the abomination that brings desolation, leave the city. The harlot is the queen of abominations, and the abomination is her consumption of blood, holy blood, the blood of martyrs. When she turns against the saints, then the city is doomed and it is time for the faithful to leave.
In the background is Jesus’ warning that a man who has been exorcised may end up inhabited by seven demons worse than himself. Babylon’s last state is worse than her first. She has been a harlot; now she is infested with demons and birds. Jesus came proclaiming the kingdom, healing and raising the dead, and casting out demons. Jesus spent much of His ministry as an exorcist. At His coming, Israel was infested with demons, especially the synagogues. Jesus expelled the demons, but when the synagogues refused to receive Him, they were reinfested. That is what happens to Babylon/Jerusalem.