“And whosoever shall not receive you, nor hear your words, when ye depart out of that house or city, shake off the dust of your feet. Verily I say unto you, It shall be more tolerable for the land of Sodom and Gomorrha in the day of judgment, than for that city.” (Matthew 10:14-15)
Now, this passage shows in what estimation the Lord holds his gospel, and, indeed, as it is an inestimable treasure, they are chargeable with base ingratitude who refuse it when offered to them.
Besides, it is the scepter of his kingdom, and therefore cannot be rejected without treating him with open contempt.
As the Lord here recommends the doctrine of the gospel, that all may receive it with reverence, and terrifies rebels by threatening severe punishment, so he enjoins the apostles to proclaim the vengeance which he threatens. But this they cannot do, unless they burn with very ardent zeal to make known the doctrines which they preach.
We must therefore hold that no man is qualified to become a teacher of heavenly doctrine, unless his feelings respecting it be such, that he is distressed and agonized when it is treated with contempt.
To shake off the dust from the feet was probably a custom then prevalent in Judea, as a sign of execration; and was intended to declare that the inhabitants of the place were so polluted, that the very ground on which they trod was infected.
That it was an ordinary custom I conjecture from our Lord’s manner of speaking of it as a thing well known.
This form of execration confirms still more what I lately mentioned, that no crime is more offensive to God than contempt of his word: for he does not enjoin them to make use of so solemn a mode in expressing their detestation of adulterers, or murderers, or any description of malefactors.
That they may not imagine this to be an idle bugbear,  Christ declares that those who reject the gospel, will receive more severe punishment than the inhabitants of Sodom.
Some view the word judgment as referring to the destruction of Jerusalem. But this is foreign to our Lord’s intention: for it must be understood as referring to the general judgment, in which both must give their account, that there may be a comparison of the punishments.
Christ mentioned Sodom rather than other cities, not only because it went beyond them all in flagitious crimes, but because God destroyed it in an extraordinary manner, that it might serve as an example to all ages, and that its very name might be held in abomination.
And we need not wonder if Christ declares that they will be treated less severely than those who refuse to hear the gospel.
When men deny the authority of Him who made and formed them, when they refuse to listen to his voice, nay, reject disdainfully his gentle invitations, and withhold the confidence which is due to his gracious promises, such impiety is the utmost accumulation, as it were, of all crimes.
But if the rejection of that obscure preaching was followed by such dreadful vengeance, how awful must be the punishment that awaits those who reject Christ when he speaks openly!
 “Afin qu’il ne semble que ce soit une menace vaine, et (cornroe on dit) seulement pour faire peur aux petits enfans;” — “that it may not seem as if it were an idle threatening, and (as we say) only to frighten young children.”
From John Calvin’s commentary on the Gospels.