The disciples misunderstand Jesus’s statement, “Watch and beware of the leaven of the Pharisees and Sadducees” (Matthew 16:5-7). What does Jesus mean by this phrase?
Following his brief interaction with the Pharisees and Sadducees, Jesus and his disciples leave and arrive at “the other side.” It is unclear if they traveled separately or where the “other side” is, since they were just in Magadan in 15:39. Perhaps they traveled from Magdala (on the south end of the lake) to Bethsaida (on the north end of the lake) since in 16:13 they are going to be well north of the lake in Caesarea Philippi.
When Jesus says, “beware of the leaven of the Pharisees,” the disciples think they have forgotten the bread; what bread? After the feeding of the 4000 there were seven baskets left over, but they seem to have forgotten to bring any of that bread with them. The disciples are thinking about dinner and realizing they forgot their supplies on the other side of the lake!
Jesus’s response indicates the disciples have missed the point (again): “O you of little faith.” As is common in the Gospel of John, the disciples understand Jesus’s reference to leaven literally, when he wanted them to understand leaven as a metaphor for what is wrong with the teaching of the Pharisees and Sadducees. They think he is chiding them for forgetting dinner!
Jesus explains the meaning of the leftover food from the miraculous feeding (16:8-11). On the one hand, Jesus’s reference to the leftover food from the feeding of the 5000 and the feeding of the 4000 might just mean, “do you guys really worry about food after what I did a few days ago?” This fits well with Jesus pointing out their “little faith.” But in the context of the leaven saying, there is more here.
Then the disciples understood, “beware of the leaven of the Pharisees,” refers to the teaching of the Pharisees and Sadducees (16:12). Leaven is something small added to flour, water, oil, etc. to make the bread rise. It is something which nevertheless has an important effect on the whole lump of dough. In Matthew 13:33, the kingdom of God is something that starts small, hidden in a lump of dough that will grow so much it will feed everyone. In this case, leaven refers to something the Pharisees and Sadducees add which spoils the whole lump of dough. (Maybe this is like adding raisins to bread dough to make raisin bread, if you do not like raisins then the whole loaf is ruined).
What is the “leaven” of the Pharisees? They are not completely wrong. In fact, the teaching of the Pharisees is really close to what Jesus teaches in terms of ethics. The Pharisees interpreted Scripture similar to Jesus and they did expect a coming Messiah. They almost have it right, but they do not have it all right.
What are the Pharisees missing? The correct understanding of who Jesus is. Peter will “get this right” in the next paragraph, Jesus is God’s Messiah, the Son of the Living God (Matt 16:16).