It was customary for Jews, returning to the territory of Israel, to remove foreign dust from their shoes and clothing in order not to defile the land. With this command, Jesus instructed the disciples to do this as a symbolic action and illustration, when the people of a certain place did not receive them. Such a town then had to understand this symbolic action as a warning and judgment if the recipients persisted.1 We see this clearly in one of the parallel passages: Matthew 10:14–15.
Later, Paul would do the same in Corinth. When the Jews rejected his message, he shook out his garments and said to them: Your blood be on your own heads! I am innocent. From now on I will go to the Gentiles
(Acts 18:6).
With this instruction Jesus prepared the Twelve that the responses would not always be positive. People would reject them and their message. When this happened, they had to reply by this symbolic act, not only terminating contact with this place, but also withholding the blessings of the kingdom of God and future judgment. Rejection of the disciples and their message was a rejection of Jesus.2
11 And if any place will not receive you and they will not listen to you, when you leave, shake off the dust that is on your feet as a testimony against them.”