Now they had forgotten to bring bread, and they had only one loaf with them in the boat. And he cautioned them, saying, “Watch out; beware of the leaven of the Pharisees and the leaven of Herod.” And they began discussing with one another the fact that they had no bread. And Jesus, aware of this, said to them, “Why are you discussing the fact that you have no bread? Do you not yet perceive or understand? Are your hearts hardened? Having eyes do you not see, and having ears do you not hear? And do you not remember? When I broke the five loaves for the five thousand, how many baskets full of broken pieces did you take up?” They said to him, “Twelve.” “And the seven for the four thousand, how many baskets full of broken pieces did you take up?” And they said to him, “Seven.” And he said to them, “Do you not yet understand?”
Understanding the gospel has never been an issue of intellect. When Jesus speaks of having eyes and ears that do not see and hear he is speaking of inner vision and hearing. This is a difficult concept for so many people because they are uncomfortable trusting that deep part of them and prefer to rely on their own understanding instead. Generally our own understanding works for us but in matters spiritual it is a hindrance and not a help.
The message that Jesus is trying to teach them is encapsulated in Proverbs when Solomon tells his readers to trust the Lord with all of their hearts and not lean on their own understanding. The leaven of the religious leaders is always about leaning on their teaching (i.e. understanding) of Mosaic Law. It is wrong because the kingdom of God is not about external rules but about laws written on a person's heart.. these laws we can trust.
Help me Lord to not rely on my own understanding but to trust you with all that is in me.