A chiasm is a literary structure where vocabulary of the first section of a passage is repeated in reverse order in the second. The center of the chiasm is typically the climax of the passage. In Luke 21:7-27 the center and climax is that when Jerusalem is surrounded (Luke 21:20), there will be days of vengeance as foretold in the Old Testament. There will be great distress upon the land itself and God’s wrath upon the Jewish people for crucifying their Messiah (Luke 21:22-23).