Shake off the dust ( τὸν χοῦν) literally, the soil—that is under your feet. St. Matthew and St. Luke use the word ( κονιορτὸν) "dust." A very significant action. The dust was shaken off as an evidence of the toil and labour of the apostles in journeying to them.
It witnessed that they had entered the city and had delivered message, and that their message had been refused. The very dust, therefore, of the place was a defilement to them. "It shall be more tolerable," etc.
This clause is omitted by the best authorities; it was probably copied from St. Matthew.