Rabanus Maurus — as excerpted in the Catena Aurea on Matthew 10:11-15

“Otherwise; The feet of the disciples signify the labour and progress of preaching. The dust which covers them is the lightness of earthly thoughts, from which even the greatest doctors cannot be free; their anxiety for their hearers involves them in cares for their prosperity, and in passing through the ways of this world, they gather the dust of the earth they tread upon. They then who have despised the teaching of these doctors, turn upon themselves all the toils and dangers and anxieties of the Apostles as a witness to their damnation. And lest it should seem a slight thing not to receive the Apostles, He adds, Verily I say unto you, it shall be more tolerable for Sodom and Gomorrah in the day of judgment, than for that city.”