John heard Jesus tell God’s people to flee from those cities.

Revelation 18:4-5

4 I heard Jesus speak from heaven. He said, “My people, flee from those cities, in order that you do not sin as the people of those cities do. If you sin as they do, I will punish you as I will punish them. 5 It is as though their sins have been piled {have piled} up to heaven, and God remembers them [DOU], so now he will punish them [MTY].”