describes how the Pharisees and Sadducees came demanding a sign from heaven.
The Pharisees and the Sadducees were both groups of Jewish priests, but greatly opposed one another. The Pharisees believed there was a coming Messiah, believed in holding onto both the oral and written traditions of the Mosaic law, and resurrection of the dead. The Sadducees, on the other hand, believed only the written law, and denied resurrection and angels.
Jesus answered them, explaining how they have enough interpretation to determine the weather. If it is a red sky in the evening, they knew it would be fair weather the next morning. If it was red in the morning, they knew it would be stormy weather. He said that though they could predict the weather, they did not have enough interpretation of the scriptures to see the very signs before their eyes.
He said that "An evil and adulterous generation seeks after a sign, but no sign will be given to it except the sign of Jonah." He then left them and departed with his disciples.
When they reached the other side, Jesus warned the disciples to beware of the "leaven" of the Pharisees and Sadducees. This confused the disciples because they did not bring any bread.
Jesus asked them, "how is it that you do not understand?" He had just fed four thousand with only seven loaves of bread, they needed no physical bread. He said that it was not bread that he was speaking about.
Then, the disciples understood what Jesus was saying. They understood that it was the teaching of the Pharisees and Sadducees that Jesus was speaking about.
Leaven, when added to dough, causes the bread to rise and become "puffed up". Leaven is a fungus that is added to the dough, not naturally found in the grain. Jesus was referring to the teachings of these groups that added their own doctrines to the Truth.
As Christians, we should ask ourselves: Do we seek after a sign? If Jesus came today in blue jeans and a T-shirt, would we recognize Him? Would we ask Him to prove Himself with a sign? Do we hold to the teachings that our preachers and evangelists give us that include more tradition than Gospel? Do they include "leaven," causing others to rise in stature and become "puffed up?" Are we part of the "wicked and adulterous generation?"