Nothing outside a man can come in and defile him. Jesus explains this to the apostles from inside a house; the Pharisees want him dead, but it's not yet his time, so he often meets indoors, in secret.

The disciples ask Jesus to explain the parable because they need God to open their eyes. 1Cor1:21-25... the wisdom of men is foolishness to God. Only the Spirit of God can regenerate the unregenerate-- nothing man can do!

Matthew 15:10-20... The Pharisees were offended by Jesus' teaching on cleanliness, and his response was, "Every plant that my heavenly Father has not planted will be rooted up. Let them alone; they are blind guides."

According to Jesus, what matters is not physical cleanliness, not social status or ethnicity, but the heart: does it belong to him? If it does, we are all one in Christ! If our heart does not belong to God, then from it will come every evil under the sun.

One thought: Mark 7 gives us 23 verses about clean vs unclean, ending with a warning about our hearts. We are really good at sin, and it's nobody's fault but our own. We have to guard our hearts! We must take every thought captive to his Word, taking in more of him and less of me!