Mark 13:15-16

15The one on the roof
Most of the roofs in the NT were flat roofs made of pounded dirt, sometimes mixed with lime or stones, supported by heavy wooden beams. They generally had an easy means of access, either a sturdy wooden ladder or stone stairway, sometimes on the outside of the house.
must not come down or go inside to take anything out of his house.
The nature of the judgment coming upon them will be so quick and devastating that one will not have time to come down or go inside to take anything out of his house. It is best just to escape as quickly as possible.
16The one in the field must not turn back to get his cloak.
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