Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man.
As a setting for this text, begin reading from verse 2. The Jews had a tradition requiring that the hands should be ceremonially washed after each contact with a Gentile. They chided Jesus and His disciples for not following the custom. Christ responded with the words of verse 11: "Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man."
In verse 15, Peter said to Jesus, "Declare unto us this parable." Please notice that this is a parable and should not be literally applied. In fact, Jesus explained the parable so that we need not speculate about the meaning. He concluded His explanation with these words, "For out of the heart proceed evil thoughts, murders adulteries, fornications, thefts, false witness, blasphemies: These are the things which defile a man: but to eat with unwashen hands defileth not a man." Verses 19, 20.
Get the picture? The Jewish leaders were upset about the custom of ceremonial washing of hands, while at the same time, they had murder in their hearts toward Christ. Jesus was exposing the absurdity of their posture. The ceremonial uncleanness was only an imagined defilement. The question of diet was not involved at all. There was no eating or drinking at the heart of the issue. It was ceremonial washing of the hands versus murder in the heart. One defiled, and the other did not -- Answers to Difficult Bible Texts, pp. 29, 30.