What does the Bible say about the leaven of the Pharisees?

In Mark 8:15, Jesus warns His disciples to beware of the leaven of the Pharisees and the leaven of Herod. This metaphor speaks to the idea that just as leaven permeates and transforms dough, the teachings and attitudes of the Pharisees can infect the hearts and minds of believers. Their reliance on signs and external rituals rather than genuine faith and humility led to a distorted understanding of God's truth. Therefore, recognizing and rejecting such corrupt influences is crucial for maintaining pure doctrine and faith in Christ.