Jesus’s fame is reaching such great heights that people are hurting each other in the press to get close to Him. But He still takes the time to make sure His disciples have the teachings they need for future ministry.
Jesus compares the Pharisees’ hypocrisy to leaven, or the action of yeast in making dough rise. Compared to the rest of the loaf, the amount of sourdough starter you add is pretty small, but it fills the whole lump with little pockets of gas, evenly distributed. In the same way, hypocrisy can start out small, but spread throughout a person’s life.
The Pharisees were very good at their outward religious expressions, but Jesus tells the disciples that everything they have done, in the dark or in inner rooms, will be revealed some day. God is not bamboozled or confounded by flattering lips and flashy lifestyles. He knows all of the inner workings of your heart, every thought, every attitude. And on Judgement Day, they will be used to condemn you if Jesus does not count you as one of His own.
Save us, for we are sinners through and through.