Jesus explains what really defiles a person- Read (Matthew 15:1-20) (Mark 7:1-23)
The Scribes and Pharisees came to Jesus and questioned him as to why his disciples transgressed the tradition of the elders by not washing their hands before eating. He in turned asked them why they transgressed the commandments of God by ignoring some aspects of it. He quoted the commandment "Honor your father and mother" and also laws related to it like those found in Exodus 21:17, Leviticus 20:9, Deuteronomy 21:18-21 which said that disobedient and arrogant children who cursed or smote their parents were to be put to death (he was not saying that they had to be doing that, but was pointing to their hypocrisy). Also some of them disliked taking care of their parents and whatever money they got, they said it was a a gift or offering consecrated to God or Corban (Mark 7:11) and so found a way to not support their parents.
Jesus remarked that Isaiah's prophesy of "Inasmuch as these people draw near with their mouths and honor me with their lips, they have removed their hearts far from me..." (Isaiah 29:13) found fulfillment in the hypocritical lives of the Pharisees.
Jesus called the people together and said, "There is nothing outside a person which going into him makes that person unclean: but the things which come out of a person are those which makes that person unclean." The disciples later asked him what that saying meant and he explained, "Do you not see that whatever goes into a man from outside is not able to make him unclean, because it goes into the stomach, and later out of the body. That which comes out of a man, that makes the man unclean. For from within, out of the heart of men, comes evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride and foolishness."
The disciples told Jesus that he had offended the Pharisees by his harsh words and Jesus replied, " Every plant, which my heavenly Father has not planted, shall be uprooted. Let them alone: they are blind leaders of the blind. If the blind lead the blind, both shall fall into the ditch."