What does Matthew 15:16 mean?

This must have been hard for the disciples to hear. Jesus sounds upset that they do not understand His comment that what goes into the mouth does not defile, only what comes out of the mouth does (Matthew 15:11). It's not shocking that the rest of the disciples wait for Peter to ask questions like this (Matthew 18:21; Mark 13:3–4; Luke 12:41). Peter seems willing to receive Jesus' pointed questions when their comprehension does not meet His expectations.

It's important to notice what follows. Jesus has just dismissed the Pharisees, Israel's religious leaders, as blind guides for their lack of understanding about the law (Matthew 15:14). Their hard-headedness means there is no point in Christ's disciples attempting to reason with them. Jesus does not dismiss His disciples, however. He takes the time to explain truth to them clearly, giving all of us a better chance to understand His meaning. This causes us, too, to be thankful for Peter's bold questions.