Then let them ... - Then Christians may know that the end is come, and should seek a place of safety. Destruction would not only visit the “city,” but would extend to the surrounding part of Judea.
The mountains - The mountains of Palestine abound in caves, a safe retreat for those who are pursued. In all ages these caves have been the favorite places of robbers, and they were also resorted to by those in danger, 1 Samuel 13:6; 1 Samuel 22:1; 2 Samuel 23:13; Joshua 10:16. In those mountains they would be safe.