I love the interchange in Matthew 15:1-20.
The scribes and Pharisees are giving Jesus grief that the apostles didn’t wash their hands before eating. Jesus turned it back on them and said:
“Why do ye also transgress the commandment of God by your tradition?”
He is asking - why are you more worried about the old traditions of ritual washings than you are about the commandments of God?
He calls them hypocrites and reminds them that Elijah prophesied they say they honor God but not in their hearts. (vs. 8)
Then we come to one of the verses (vs 14) that I think shows a bit of humor on the part of Jesus when he tells the disciples:
“Let them alone: they be blind leaders of the blind. And if the blind lead the blind, both shall fall into the ditch.”
In my mind it goes something like this:
“Meh, leave em’ alone.”
*waves hand of indifference*
“Blind leading the blind; they’ll fall in the ditch.”
Then Jesus explains the parable he said to the scribes and Pharisees.
Basically, what you put into your mouth comes out the other end and doesn't defile you. What comes out of your mouth, on the other hand, comes from your heart and can defile you if your heart has evil thoughts.
It all comes back to what is in your heart.