Jesus taught his disciples that nothing that enters us from without can make us impure. Rather, the malice and bad thoughts in our hearts that come out in our words and actions make us impure. This is a call to us to let go of the superficial things of religion and examine our own hearts and actions.
Based on Mark 7:14-23:
Jesus called the crowd again and said to them, ‘Listen to me, all of you, and understand: there is nothing outside a person that by going in can defile, but the things that come out are what defile.’
When he had left the crowd and entered the house, his disciples asked him about the parable. He said to them, ‘Then do you also fail to understand? Do you not see that whatever goes into a person from outside cannot defile, since it enters, not the heart but the stomach, and goes out into the sewer?’ (Thus he declared all foods clean.) And he said, ‘It is what comes out of a person that defiles. For it is from within, from the human heart, that evil intentions come: fornication, theft, murder, adultery, avarice, wickedness, deceit, licentiousness, envy, slander, pride, folly. All these evil things come from within, and they defile a person.’
(New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org)