It is not what goes into us that defiles us it is what comes from our broken hearts. This is part of the essential theme of the Gospels. Our hearts are broken. From our damaged hearts comes all manner of selfish, self serving and prideful behavior. Human beings are in need of a "heart transplant". We need to be transformed from the inside out. All the talk about being "born again" or being "saved" only scratches the surface of what Jesus was actually about. Christ followers are being remade from the inside out. We don't wait for eternity to be made into new people . . . we begin the journey now.
The Kingdom of the heavens is not about food and drink and what we do or what we don't do. It is about servants becoming sons and daughters. It is about the restoration of the image and likeness of God in every human being. Looking at other stories and teachings in the Gospel we can see that "what proceeds from the heart" is a the same teaching as the good tree bringing good fruit. The Gospel is not giving us a new rule book -- rather the Gospel is showing what the evidence of a heart transplanted Christ follower. The transformation of a human into sons and daughters of God is a life long process that requires us to get close to the one we are to become like.