Matthew 24:20 - Ellicott's Commentary On The Whole Bible

Pray ye that your flight ... — Rules were given for flight where the conditions lay within their own power. Other incidents which lay outside their will might lawfully be the subjects of their prayers. It is characteristic of St. Matthew, as writing for Jews, that he alone records the words “nor on the Sabbath day.” Living as the Christians of Judæa did in the strict observance of the Law, they would either be hindered by their own scruples from going beyond a Sabbath day’s journey (about one English mile), which would be insufficient to place them out of the reach of danger, or would find impediments — gates shut, and the like — from the Sabbath observance of others.