Jamieson, Fausset and Brown on Matthew 10:14

14. And whosoever shall not receive you, nor hear your words, when ye depart out of that house or city--for possibly a whole town might not furnish one "worthy."

shake off the dust of your feet--"for a testimony against them," as Mark and Luke add (Mr 6:11; Lu 10:11). By this symbolical action they vividly shook themselves from all connection with such, and all responsibility for the guilt of rejecting them and their message. Such symbolical actions were common in ancient times, even among others than the Jews, as strikingly appears in Pilate (Mt 27:24). And even to this day it prevails in the East.