From: Matthew 15:1-2, 10-14
 Then Pharisees and scribes came to Jesus from Jerusalem and said,  "Why do your disciples transgress the tradition of the elders? For they do not wash their hands when they eat."
 And he called the people to him and said to them, "Hear and understand:  "Not what goes into the mouth defiles a man, but whatcomes out of the mouth, this defiles a man."  Then the disciples came and said to him, "Do you know that the Pharisees were offended when they heard this saying?"  He answered, "Every plant which my heavenly Father has not planted will be rooted up.  Let them alone; they are blind guides. And if a blind man leads a blind man, both will fall into a pit."
10-20. Our Lord proclaims the true meaning of moral precepts and makes it clear that man has to answer to God for his actions. The scribes' mistake consisted in concentrating on externals and not giving pride of place to interior purity of heart. For example, they saw prayer in terms of exact recital of fixed forms of words rather than as a raising of the soul to God (cf. Mt 6:5-6). The same thing happened in the case of dietary regulations.
Jesus avails of the particular cases dealt with in this passage to teach us where to find the true center of moral action: it lies in man's personal decision, good or evil, a decision which is shaped in his heart and which then is expressed in the form of action. For example, the sins which our Lord lists are sins committed in the human heart prior to being acted out. In the Sermon on the Mount he already said this: "Every one who looks at a woman lustfully has already committed adultery with her in his heart" (Mt 5:28).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.