After the Sadducees had been silenced, the Pharisees take another stab at trying to trap Jesus with a question concerning the Law.  He reveals once again that they their hearts are far from Him - that in all their attention to the Law, they miss Jesus - they miss the heart of it all. Jesus follows this up with a question of his own - this one concerning the David's Son - not only do they not love God, they don't because they don't know him.