“Then Jesus left the Pharisees and went in the boat to the other side of the lake. His followers had only one loaf of bread with them in the boat; they had forgotten to bring more. Jesus warned them, ‘Be careful! Beware of the yeast of the Pharisees and the yeast of Herod.’ His followers discussed the meaning of this, saying, ‘He said this because we have no bread.’” (Mark 8:13-16 NCV)

In the Bible, yeast is often a metaphor for pride and arrogance. Why? When you put yeast in dough, what does it do? It puffs it up, and if you put in too much, it blows it up.