In sending out his disciples to extend our Christian way of life he told them to take no money or food for the journey. Instead of sending them out as self-sufficient big shots, he wanted them to look like people who needed friends. He wanted them to throw themselves on the hospitality of the people of those towns.
Of course, that won’t always work. At times the disciples found themselves among mean-spirited people who scorned them. In that case, Jesus told them to engage in the reversal of one of their favorite rituals.
I refer to what Jews did on entering Jerusalem’s temple. They would halt, then shake the dust off their sandals. They did that to acknowledge the temple to be a holy ground, seeing it as akin to the plot bearing the burning bush in the Exodus story of Moses.
Jesus, by prescribing a reversal of that practice, telling the disciples to shake the dust off their sandals on exiting an inhospitable town, asked the to see the whole wide world as God’s holy place, not to be contaminated by dust from an inhospitable town.