Jesus is very clear that what you do on the outside is not what defiles you. Your heart is either defiled or not. The leading spiritual indicator which will show the condition of the heart is the words we speak. Everything comes from the heart (Proverbs 4:23). This passage provides a long list of sins that come from the heart. But, words come first. What do my words say about the condition of my heart?
Jesus engaged in conflict with Pharisees and scribes; he summoned the crowd to listen in; the disciples received personalized Q & A. Flexibility in communication is one key, humanly speaking, of Jesus' effectiveness.