John explores three different ways of reading the gosple for this day (Matthew 15: (10-20) 21-28).
The first is that Jesus is just rude.
The second that here we see both Jesus and the early Christian community struggling with the universal implications for what Jesus was teaching and living out. To read it in this way people need to keep in mind some information about how the New Testament came to be.
Thirdly I want to place this story with the what Jesus is talking about before it, and to suggest this is used by Matthew as an example of what Jesus is saying, that it is not obedience to the law that makes one clean, but what comes from ones heart.