Either as a testimony to the earthly toil which they had in vain undergone for them, or to shew that so far from seeking any thing earthly from them, they suffer not even the dust from their land to cleave to them. Or by the feet is meant the very labour and walking to and fro of preaching; but the dust with which they are sprinkled is the lightness of worldly thoughts, from which even the greatest teachers cannot be free. Those then who have despised the teaching, turn the labours and dangers of the teachers into a testimony of their condemnation.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).