Charles Spurgeon Commentary Matthew 24:17-18

"let him that is on the housetop not go down to take out things that are in his house: and let him that is in the field not return back to take his cloak." — Matthew 24:17-18 (ASV)

Let him which is on the housetop not come down to take any thing out of his house: Neither let him which is in the field return back to take his clothes.

They were to flee in all haste the moment they saw the Roman standards.