IO could be wrong, but "shake off the dust of your feet." is not synonymous with "Harangue them into submission."
While I may be an agnostic, I know good advice when I hear it.
Good day to you.
If you get interested in the Bible, try using the tools which have proven effective in understanding the Bible scenes. To whom does a passage speak and of whom? For what 'dispensation' is the passage offered to edify? What timing is evident in the passage meaning?
It is evident that you are of better than average intelligence and have the capabilities to study without immediate teaching. Enjoy your journey through Scriptures because the Bible is the only book I know of which guarantees the author will enlighten you to the meaning He intended if you will but ask for His guidance in same.
When you do get deeper into scripture you will find a particular passage which states that Christians are to contend for the Gospel, not merely talk about Jesus. We are even admonished to put on armor for the daily 'contending'. Jesus even went so far as to instruct that there had arrived a time to sell something and buy a sword. When He sent the first wave out to the Jewish homes, he told them to take nothing along for their maintenance, but the second time He sent His disciples forth He gave more explicit and directed instructions.
BYW, that dust was meant to be a witness that the folks in that house had rejected the message sent from The Lord, the Jewish folks in that house. The threshold of the Jewish home had significance beyond merely an entry to the dwelling.