What does Genesis 19:23 mean?

The Lord's judgment is coming on the cities of Sodom and Gomorrah—actually, upon the entire region occupied by these two depraved cultures. Prior to this, and for the sake of our own understanding, God even allowed Abraham to set the limit of Sodom's rescue: 10 righteous people. This, despite being such a low standard, is a test this culture could not pass. Lot and his family were living in Sodom, but God has mercifully removed them, allowing them now to escape what is coming by hiding out in the small, nearby city of Zoar. In fact, the Lord has agreed not to destroy Zoar for their sake.

In the previous verse, it was made clear to Lot that the judgment would not begin until his family reached Zoar. Now they have arrived, sometime after sunrise. Just as the family makes it to safety, God enacts one of his most spectacular instances of earthly wrath. In a moment symbolic of God's ultimate defeat of sin and evil, the people of Sodom and Gomorrah will be annihilated in a rain of fire.