From Matthew 10:14. Jesus sends some of his disciples out to preach the "Good News" to the "lost sheep of Israel". Among His many marching orders: "If anyone will not welcome you or listen to your words, shake the dust off your feet when you leave that home or town" (NIV). That is to say, don't be a masochist and belabor your point (unless, of course, you just like toying with folks). Just go. Wash your hands of the situation, you've done your bit. Move along; God sorts 'em out.