Then they understood that he was not saying to beware of the yeast of bread, but of the teaching of the Pharisees and Sadducees.
At last the disciples grasp the deeper, non-material meaning of Jesus’ words. They understand that by “leaven” Jesus meant not the bread, but the false teachings of the Pharisees and Sadducees, which, though they had a religious appearance, did not spring from true faith and could gradually corrupt their way of thinking. This moment is important, because it shows the course of their maturing and the fruit of Jesus’ patient instruction.