"Be on your guard against the yeast of the Pharisees, which is hypocrisy."
Beverly used to make bread. Someone gave her some "starter." It was basically yeast that had been passed down from one person to another for who knows how long. It just continued to multiply.
The yeast of the Pharisees is thousands of years old. And it is real easy to pass down. It is hypocrisy. Let me clarify something here: It is not hypocritical to try to be something -- and occasionally fail. Hypocrisy is pretending to be something you never intend to be. It is a question of motive.
Example: The way Jesus described the Pharisees' fasting. They would make themselves look haggardly, but they had no intention of being broken in heart. It was just a pretense.
Let's beware of the yeast of the Pharisees. It is alive and well today. But God is not fooled by it. In fact, Jesus says, "There is nothing consealed that will not be disclosed, or hidden that will not be made known." In other words, our motives will be revealed. So, God -- create in me a clean heart! And renew a right spirit within me!