Mark 7:20

And he said, That which cometh out of the man, that defileth the man.

Jesus spoke these words when Pharisees and certain scribes confronted Him because His disciples ate bread without ceremonial washing of hands. The purification rules at issue were numberless rabbinical precepts that professedly were designed to guard the law of God but encumbered it, were regarded as more sacred than the law itself, and when the two collided were given preference over the commandments given from Sinai. Neglect of those rules was counted heinous sin, while keeping them made life one long struggle against ceremonial defilement in an endless round of washings. Christ and His disciples did not observe these ceremonial washings, showing that defilement does not come from neglecting traditional precepts about purification, and that outward trifling distinctions and observances God has not required do not defile.

Those unrequired outward observances turn attention away from the great principles of God's law. Defilement instead comes from what comes out of a person from within, from the heart. Evil thoughts and conduct arise from this inner source, which becomes corrupt when wicked thoughts are allowed to strengthen and prevail.