Matthew 15:16

And Jesus said, Are ye also yet without understanding?

The question belongs to the dispute over ceremonial handwashing, in which the religious leaders treated human rules of purification as more sacred than God's commandments. Jesus and His disciples did not observe those washings.

The question is a rebuke to Peter and the disciples for still lacking understanding when Peter asked Him to explain the parable about defilement. The rebuke means they should have grasped that pollution is moral rather than ceremonial. What enters the mouth goes into the belly and is cast out, so it does not defile, while what comes out of the mouth comes from the heart and defiles a person. Out of the heart come evil thoughts, murders, adulteries, fornications, thefts, false witness, and blasphemies, and these are what defile, but eating with unwashed hands does not defile.