Casting Pearls before Swine

Do not give what is holy to dogs, and do not throw your pearls before swine, lest they trample them under their feet, and turn and tear you to pieces. (Matthew 7:6)

In biblical times dogs were seldom kept as household pets in the way they are today. Except for those used as working animals to herd sheep, they were largely half-wild mongrels that acted as scavengers. They were dirty, greedy, snarling, and often vicious and diseased. They were dangerous and despised.

It would have been unthinkable for a Jew to have thrown to those dogs a piece of holy meat that had been consecrated as a sacrifice in the Temple. Some parts of those offerings were burned up, some parts were eaten by the priests, and some would often be taken home and eaten by the family who made the sacrifice. The part left on the altar was the part which was consecrated exclusively to the Lord, and therefore was holy in a very special way. If no man was to eat that part of the sacrifice, how much less should it be thrown to a bunch of wild, filthy dogs. Such an act would be the height of desecration. . . .

http://www.macarthurcommentaries.com