5Later, after they crossed to the other side of the lake, the disciples discovered they had forgotten to bring any bread.6“Watch out!” Jesus warned them. “Beware of the ayeast of the Pharisees and Sadducees.”7At this they began to argue with each other because they hadn’t brought any bread.8Jesus knew what they were saying, so he said, “You have so little faith! Why are you arguing with each other about having no bread?9Don’t you understand even yet? Don’t you remember the 5,000 I fed with five loaves, and the baskets of leftovers you picked up?10Or the 4,000 I fed with seven loaves, and the large baskets of leftovers you picked up?11Why can’t you understand that I’m not talking about bread? So again I say, ‘Beware of the byeast of the Pharisees and Sadducees.’ ”
Remember when Jesus used yeast as a comparison to the Kingdom of God? Yeast is something very small that spreads and changes a lot of dough. Well, small evil things can have the same effect. A little here of a little there, and suddenly we are changed. The Pharisees and the Sadducees were the promoters of rituals and rules, not faith. They believed that being right with God was something that could be attained through human effort, not faith alone.