". . . Do you not see whatever goes into the man from the outside cannot defile him," Mark 7:18
The only time Jesus ever had conflict was with religious people. When Jesus spoke these words, it was the most radical statement the religious leaders had ever heard. More so than aspects of elaborate hand washings, or how traditional law can lead to disobedience.
What Jesus says here is startling. No Jew ever believed this. The Orthodox Jew strictly followed Leviticus 11, which contains a long list of animals that are considered unclean and may not be used for food. In one clean stroke, Jesus is wiping away the system of laws they had so long lived under.
In effect, Jesus was saying that things can't be clean or unclean in any religious sense. Only an individual can be defiled, and what defiles a person is their own actions, which is a product of the heart. In one shocking statement, Jesus declares the whole thing irrelevant. Uncleanliness has nothing to do with what is taken into the body, but everything to do with what comes out of the heart.
The dietary laws were of no use to Jesus. Food that goes into the body is eliminated naturally. What must be dealt with are the contents of the heart. Every outward act is preceded by an inward act of choice.
Jesus is surprised that His disciples are so clueless about this truth. His tone shifts to one of rebuke, so He states it, emphatically, by giving an x-ray of the human heart and what it's capable of producing. Jesus reveals what a cesspool the heart is. Jesus shows us that the human heart is actively wicked.
We, as His disciples, must see to it that we don't over estimate our personal goodness, or under estimate our potential for badness. It's for this reason scripture directs us to guard the heart, for out of it flows the issues of life.
Take inventory of the contents of your heart, and deal with it.