"What goes into a man's mouth does not make him 'unclean,' but what comes out of his mouth, that is what makes him 'unclean.' "
I think this is one of my favorite chapters in the book of Matthew. Jesus is very firm with the Pharisees...they were so focused on the outside of the body...what was clean or unclean. They never considered the heart.
Although the Pharisees were experts in God's Law, they lacked proper understanding of the purpose of the Law. Most importantly, they lacked faith in God.
The Pharisees had faith in the religious system Jesus pointed to God who was beyond the system they worshiped.
I have to laugh at the disciples here...they say to Jesus in verse 12: "Do you know that the Pharisees are angry because of what you said?" And Jesus responds with "Stay away from the Parisees; they are blind leaders. And if a blind person leads a blind person both will fall into a ditch!"
But the disciples still don't get it! The ask Him to explain what He means! This must be where the phrase comes from "It's like the blind leading the blind". Jesus is trying so hard to help them understand that God doesn't care about our outer self. It is the heart He is looking at. The condition of the heart reveals the true life of that person! And the condition of the heart comes out in the very words we speak! If we have a bitter uncaring heart...our mouths will reveal it in all it's glory!
When you obey certain rules today, stop and think through why you obey them. "I don't speed because...I don't cheat on my income taxes because...I honor my family because..." What condition is your heart in today? Will it reveal Jesus? I know I have to pray everyday that the condition of my heart is full of God's love for me!