Matthew 16:5 - 12

5 Now when His disciples had come to the other side, they had forgotten to take bread.

6 Then Jesus said to them, “Take heed and beware of the leaven of the Pharisees and the Sadducees.”

7 And they reasoned among themselves, saying, “It is because we have taken no bread.”

8 But Jesus, being aware of it, said to them, “O you of little faith, why do you reason among yourselves because you have brought no bread?

9 Do you not yet understand, or remember the five loaves of the five thousand and how many baskets you took up?

10 Nor the seven loaves of the four thousand and how many large baskets you took up?

11 How is it you do not understand that I did not speak to you concerning bread?—but to beware of the leaven of the Pharisees and Sadducees.”

12 Then they understood that He did not tell them to beware of the leaven of bread, but of the doctrine of the Pharisees and Sadducees.

Jesus and the disciples crossed the sea in a boat to the other shore, they had been on the western shore of the Sea of Galilee near the city of Magdala, so now they are on the eastern side of the sea. Apparently the disciples had forgotten to bring provisions. (Mark 8:14, says they had taken one loaf of bread with them.) Jesus is going to use this as a basis for a test of their faith in Him as one who could and would take care of them.

Without mentioning bread, Jesus warns the disciples to watch and be careful of the leaven of the Pharisees and Sadducees, they were aware of how evil these two groups of Jews were.

They do not see any logical connection between leaven and these two groups of Jews so they consider that Jesus is chastising them because they did not bring provisions for their work in an uninhabited area.

Jesus chastises their amount of faith because they were worried about their lack of provisions. Even if there were no practical prospects of having food for there present time, they should have had enough confidence in Jesus because of their experiences with Him to believe He would not let anything serious happen to them.

When Jesus mentioned the leaven of the Pharisees and Sadducees, the disciples thought He was chastising them for forgetting to bring provisions. Jesus, points out they should have remembered the miracles of feeding the 5000 and the feeding of the 4000 and the great amount of leftovers, He wants them to think, if He was considering food, why worry when He could take care of that problem. Their belief should have considered that fact.

Jesus statement told them He was not considering bread so they then understood he was speaking figuratively.

When they understand Jesus is speaking of the false doctrines of the Pharisees and the Sadducees. They should understand the problems these two groups cause for followers of God.

The two groups are as such:

Pharisees taught a false doctrine of traditions being equal to the Word of God.

Sadducees did not believe in an eternal life of either heaven or hell.

This is the leaven of the Pharisees and the Sadducees.