Matthew 15:17
Do not ye yet understand, that whatsoever entereth in at the mouth goeth into the belly, and is cast out into the draught? Do not ye yet understand, that whatsoever entereth in at the mouth goeth into the belly, and is cast out into the draught?
The saying was spoken in a controversy over ceremonial washing of hands before eating. The washings demanded were rules added by rabbis, not commands given by God, yet they were treated as more sacred than God's law itself, turning minds away from its central principles. After the Pharisees took offense at the teaching, Peter asked for the parable to be explained, and the answer came with a rebuke for still failing to understand.
What goes in at the mouth passes into the belly and is afterward cast out of the body. For that reason neither food in itself nor eating with unwashed hands contrary to human tradition about eating makes a person defiled. Defilement is from within, coming out of the heart through the mouth in evil thoughts, murders, adulteries, fornications, thefts, false witness, and blasphemies.