Matthew 7:6

Do not give what is holy to dogs. Jews did not think of dogs as "man's best friend." Dogs roamed in snarling packs and were scavengers. They were "unclean" by religious law, and they came to be the symbol of cruel, inhuman people who opposed every good thing. It is useless to teach spiritual things to such a person. Do not throw your pearls in front of pigs. Pigs were also religiously "unclean." Having no use for pearls, they would savagely attack those who threw them. Symbolically, there is a type of mind which would attempt to destroy the one who spreads Truth. It is our duty to help all people and save as many as possible, but there is a type of person whom we cannot reach. [But avoid "judging" who this person is.]