When His disciples had come to the other side, they had forgotten to take bread. Then Jesus said to them, "Take heed and beware of the leaven of the Pharisees and the Sadducees." Matt. 16:5, 6, NKJV.
Somebody is always messing up. This time no one had brought any bread. That worried the disciples greatly, and Jesus knew it. So while they had their minds on bread, He told them to beware of the leaven of the Pharisees and Sadducees, referring to their false ideas about true religion, including their erroneous ideas of the mission of the Messiah. After all, all of them were looking for a powerful earthly king rather than a suffering servant. That teaching, as we saw at the feeding of the 5,000 posed a genuine temptation to the disciples. Such thought could easily continue to permeate their minds, much as yeast spreads through dough.
Yet that view of Messiah's function would soon be shattered as Jesus became the Lamb of God. He needed to implant the true leaven in their minds to prepare them for that event and their own future work.
Jesus had a message for them, but all they could think about was their stomachs. That brought forth what may be Jesus' harshest comment on their dullness: "O men of little faith, why do you discuss among yourselves the fact that you have no bread? Do you not yet perceive? Do you not remember the five loaves of the five thousand, and how many baskets you gathered?...How is it that you fail to perceive that I did not speak about bread?" (Matt. 16:8-11, RSV). At that point, they finally realized that He had in mind the leaven of the false teachings that they had grown up with and with which they had filled their minds.
One significant fact to note is that Jesus links the Pharisees and Sadducees together. They were opponents in Jewish religious and political life, standing for radically different ideas. But in Jesus they had found a common enemy who threatened the status quo. A powerful enemy makes strange bedfellows. Their unity will last up to the Crucifixion.
As we meditate today, we need to remember the lesson of the leaven and how powerful extra-biblical philosophies are in distorting our beliefs. Above all, we need to keep our eyes turned to Jesus and His Word.