 you can be sure that on judgment day, they will be mighty sorry, but it's of no concern to you. I don't know if that's the best translation. It sounds rather oddly indifferent to the fate of others. Because the shaking of the dust was a symbolic act of repudiation of Jews in pagan land. In other words, if someone rejects you, or does not accept the peace that you offer, you still must live a life of peace.