John Chrysostom

"But they shook off the dust of their feet against them, and came unto Iconium." Here now they used that terrible sign which Christ enjoined, "If any receive you not, shake off the dust from your feet"; but these did it upon no light ground, but because they were driven away by them. This was no hurt to the disciples; on the contrary, they the more continued in the word.

Homily on Acts 30 ↗

Theophylact of Ohrid

They did not do this without reason, but because they had been driven out by the Jews.

Commentary on Acts ↗

Oecumenius

They fulfill what the Lord commanded them, saying: "If anyone does not receive you, shake off the dust from your feet." (Matt. 10:14, Mark 6:11, and Luke 9:5) But these not only did not receive them, but even drove them out of their borders, which is worse. For the Lord does not wish his disciples to have even the dust on their feet from the land of wicked people, thereby showing that they had gained nothing from the disobedient. The dust is a token of the toil which they endured on their behalf. [CHRYSOSTOM]

Commentary on Acts ↗

Bede

But shaking the dust off their feet against them, they went to Iconium. The dust is shaken off the feet according to the precept of the Gospel as a testimony of their labor, that they entered their city and that the apostolic preaching reached them; or the dust is shaken off so that they take nothing from them, not even what is necessary for sustenance, who have rejected the Gospel.

Commentary on Acts ↗