What does Matthew 24:20 mean?

When the sign predicted by Daniel (Matthew 24:15) finally happens, those in Jerusalem should run for their lives (Matthew 24:16–19). He has spoken urgently, saying that those on their rooftops should not go back into their homes for supplies and those in the fields should not go back for their cloaks. They should simply run—just get away. Later, Jesus will comment that the danger triggered by this event will be enough to threaten the entire human race (Matthew 24:21–22).

Christ added a note of sadness for the vulnerable people who will be caught up in those days. Keeping with that theme, He commands His disciples to pray that they won't have to try to make the journey in winter or on a Sabbath day. Winter, of course, would make travel more difficult generally, especially by causing river- and creek-beds to be swollen with water and tough to cross. On a Sabbath day, it would be hard to find help along the way from faithful Jews. It would also make large groups of Jewish people who would normally be avoiding activity easier to spot.

Some Bible teachers point to the events of the attempted Jewish rebellion against Rome in AD 70 as the full or partial fulfillment of Jesus' words here. That rebellion led to a terrible siege and the eventual destruction of Jerusalem and the temple. Many Jewish people did run from Jerusalem for their lives, and many were slaughtered in the attempt. However, the temple was ruined at the end of that war, not the beginning of it. Jesus' words seem a better fit for the very last days prior to His second coming (Revelation 19:11–15).