In this passage, Jesus is talking about the human heart. The religious leaders were upset about his disciples not following the proper tradition and procedures, but Jesus tells them that being "unclean" does not come from not following tradition.
He says that being unclean comes from within, from the human heart.
There are so many ways that the human heart can be the source of pain, evil, destruction, and all the things Jesus mentioned. We've seen that this week with Afghanistan, Haiti, anytime we watch the news.
But as we have seen this week as well, the human heart is a source of beauty, generosity, and grace.
Let us focus on our own hearts, and make them places of gratitude and grace from within. Only then can we begin to change the world.