Bede

Now having described the reception from different houses, he teaches them what they ought to do in the cities; namely, to have intercourse with the good in all, but to keep from the society of the wicked in every thing; as it follows, But into whatsoever city ye enter, and they receive you, eat such things as are set before you.

Either as a testimony to the earthly toil which they had in vain undergone for them, or to show 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.

The men of Sodom, although they were hospitable in the midst of all their wickedness of soul and body, yet were there no such guests found among them as the Apostles. Lot indeed was righteous both in seeing and hearing, yet he is not said to have taught or worked miracles.

Into whatever city you enter and they do not receive you, going out into its streets, say: Even the dust that clings to us from your city, we wipe off against you. Either as a witness to the earthly labor they undertook for them in vain, or to show that they sought nothing earthly from them, to the extent that they would not allow even the dust from their land to adhere to them. Alternatively: The feet of the disciples signify the very work and journey of preaching. The dust with which they are sprinkled is the lightness of earthly thought, from which even the highest teachers cannot be exempt when they incessantly attend to the healthful cares for the listeners, and as if along the roads of the world, they gather the dust of the earth scarcely with a single heel. Therefore, those who receive the word turn the afflictions and cares of the teachers, which they endured for them, into a testament of humility. But those who spurn the teaching transform the labors and dangers and weariness of the solicitude of the teachers into a testimony of their condemnation. And this is the dust that is wiped off against those who scorn the Gospel, and from which the feet of the evangelists are commanded to be washed by good listeners, or even narrated to be washed by the Savior himself.

For if the miracles that were done in you had been done in Tyre and Sidon, they would long ago have repented sitting in sackcloth and ashes. We see today the fulfillment of the Savior's saying, because indeed Chorazin and Bethsaida did not want to believe with the Lord present. Tyre and Sidon, however, were once friendly to David and Solomon, and later believed in the disciples of Christ who were preaching. And they accepted the faith with such devotion, that all the citizens of Tyre, accompanying Paul the apostle as he was leaving, with their wives and children, followed him outside the city, and in a most beautiful spectacle, such a multitude of people escorted a very few guests, but the most illustrious for Christ's faith, up to the ships to bid farewell. But why the gospel was not preached to those who could believe earlier, truly it is to know for those to whom it was preached, while the Jews did not want to believe, it is to know for Him, whose all ways are mercy and truth (Psalm XXIV). Surely what the Lord says: Sitting in sackcloth and ashes they would have repented: in sackcloth, which is woven from goat hairs, signifies the harsh memory of the pricking sin, with which the left part is to be dressed on the day of judgment; in ashes, however, demonstrates the consideration of death, through which the whole mass of the human race is to be reduced to dust. Moreover, in the sitting denoted the humiliation of own conscience. Of which the Psalmist: Arise after you have sat (Psalm CXXVI), which is to say: Humble yourselves under the mighty hand of God, so that He may exalt you in the time of visitation (1 Peter V).

Chorazin, Bethsaida, and Capernaum, Tiberias also which John mentions, are cities of Galilee situated on the shore of the lake of Gennesaret, which is called by the Evangelists the sea of Galilee or Tiberias. Our Lord thus mourns over these cities which after such great miracles and wonders repented not, and are worse than the Gentiles who break through the law of nature only, seeing that after despising the written law, they feared not to despise also the Son of God and His glory. Hence it follows, For if the mighty works had been done in Tyre and Sidon which have been done in you, they had a great while ago repented sitting in sackcloth and ashes, &c. By sackcloth, which is woven together from the hairs of goats, he signifies a sharp remembrance of previous sin. But by ashes, he hints at the consideration of death, by which we are reduced to dust. Again, by the sitting down, he implies the lowliness of our conscience. Now we have seen in this day the word of the Saviour fulfilled, since Chorazin and Bethsaida, though our Lord was present among them, believed not, and Tyre and Sidon were friendly both to David and Solomon, (1 Kings 5.) and afterwards believed in the disciples of Christ who preached the Gospel there.

This sentence admits of two meanings: Either for this reason shalt thou be thrust down into hell, because thou proudly resisted My preaching; that in truth she might be understood to have raised herself up to heaven by her pride. Or, because thou art exalted to heaven by My dwelling in thee, and by My miracles, shalt thou be beaten with more stripes, since even these thou refusedst to believe. And that no one should suppose that this interpretation applied only either to the cities or the persons who, seeing our Lord in the flesh despised Him, and not to all also who now despise the words of the Gospel, He proceeds to add these words, He that heareth you, heareth me.

That is, that every one indeed on hearing or despising the preaching of the Gospel might learn that he is not despising or hearing the mere individual preacher, but our Lord and Saviour, nay the Father Himself; for it follows, And he that despiseth me, despiseth him that sent me. For the Master is heard in His disciple, the Father honoured in His Son.

It may also be understood as follows, He who despiseth you, despiseth me, that is, he who shows not mercy to one of the least of My brethren, neither shows it to Me. But he who despiseth me, (refusing to believe on the Son of God,) despiseth him that sent me. (Matt. 25:40.) For I and my Father are one. (John 10:30.)

He says not, 'I see now,' but referring to past time, I saw, when he fell. But by the words as lightning, He signifies either a fall headlong from the high places to the lowest, or that now cast down, he transforms himself into an angel of light. (2 Cor. 11:14.)

That is, I give you the power of casting out every kind of unclean spirit, from the bodies possessed. And as far as regards themselves, He adds, And nothing shall hurt you. Although it might also be taken literally. For Paul when attacked by a viper suffered no injury. (Acts 28:5.) John having drunk poison is not harmed by ita. But I think there is this difference between serpents who bite with the teeth, and scorpions who sting with the tail, that the serpents signify men or spirits raging openly, scorpions signify them plotting in secret. Or serpents are those which east the poison of evil persuasion upon virtues just beginning, scorpions which go about to corrupt at last virtues which have been brought to perfection.

They are forbidden to rejoice in the subjection of the spirits to God, since they were flesh; for to cast out spirits and to exercise other powers is sometimes not on account of his merit who works, but is wrought through the invocation of Christ's name to the condemnation of those who mock it, or to the advantage of those who see and hear.

As if he said, It becomes you to rejoice not in the putting down of the evil spirits, but in your own exaltation. But it would be well for us to understand, that whether a man has done heavenly or earthly works, he is thereby, as if marked down by letter, for ever fixed in the memory of God.