Luke 10:10

But into whatsoever city ye shall enter, and they receive you not, go out into the streets thereof and say, Even the dust from your city, that cleaveth to our feet, we wipe off against you: nevertheless know this, that the kingdom of God is come nigh.

No gospel mission has any valid purpose beyond that of giving men the opportunity to hear and know the truth. The foregone certainty that countless souls shall reject the message cannot invalidate or change the message, nor impose any further responsibility upon the messengers beyond that of faithfully declaring the word of God. In these instructions, Jesus clearly recognized the right of cities to reject the truth if they wished to do so; but such a rejection entailed also their suffering of the penalties and consequences of their choice. The message was exactly the same to those who received and those who rejected God's messengers: "The kingdom of God is come nigh."

The carryover from this Scripture has wide applications in the church of all ages. God does not command that any specific individual or city be "won for the Master," but rather that the message be proclaimed in its full integrity; the rest is left up to the hearer.

We wipe off against you ... Adam Clarke has the following with regard to this:

The Jews considered themselves defiled by the dust of a heathen country, which was represented by the prophets as a "polluted land," Amos 7:17, when compared with the land of Israel, which was considered as a "holy land," Ezekiel 14:1; therefore, to shake the dust of any city of Israel from off one's clothes or feet was an EMBLEMATICAL action, signifying a renunciation of all further connection with them, and placing them on a level with the cities of the HEATHEN. See Amos 9:7.[13]

The practice of this symbolical action was continued into the apostolic age; Paul and Barnabas, for example, "Shook off the dust of their feet against them and came unto Iconium" (Acts 13:51). The relevance of this for present-day missionaries lies in the fact that if God's word is rejected in one place, the message should then be declared in another. Of course, this is also true regarding individuals; and no preacher of the word should consider it his divine mission to nag any man into the kingdom of God.