How do you respond when people reject the faith? Do you get upset? Do you just ignore it? Do you argue with them? There are times when we need to work to give a clear explanation of the faith to those who do not believe. Yet, at the same time, we should not put all our efforts into one person who refuses to listen to the truth of God. It is a hard balance to achieve, but we are called to do our best to find that very balance.
In today's gospel reading, Jesus tells the Apostles to move on when people reject the gospel. Sadly, many people today do not move on at all. Rather, a number of Catholics (sadly) will water down the gospel so that pagans will accept it (which is what many Catholics have done to the pastoral encouragements of the second Vatican council). That is a grave sin. It is the same as lying to the world about what the gospel actually is. If we change the truth, it is no longer the truth.
Even if the world rejects the truth, we still are required to give it the truth. This is why Jesus said to move on to others when someone rejects the gospel. We are taking away the truth from those we are speaking to if we compromise it, and we are also keeping the truth from someone else who may be willing to listen. Our Lord always has good reason in the counsel He gives us.
Yes, there will be times when we must keep working to explain the faith to someone because he is growing in his understanding; we do not reject people for moving slower than we want. Yet, if there is no progress in the faith, and the person will not hear the truth, Jesus wants us to "move on". Speaking the truth can be a scary thing, but the Holy Ghost is there to help us. Trust God, the Father, Son, and Holy Ghost, to be with you and help you to tell others what they need to hear, but never compromise the truth. And, if they refuse to listen, seek out others who will.