In Matt 16:5-11 Jesus warmed his disciple to “beware of the leaven of the Pharisees.” The “leaven” that concerned him was the teaching of the Pharisees and Saducees. What was their teaching? It was religious pride, pride in their virtues. I will go to heaven because I am a good person, because I have tried hard, because I am sincere, at least as sincere as the average person. 

But Jesus also used “leaven” in another sense. He called the gospel leaven. “The Kingdom of heaven is like leaven that a woman took and hid in three measures of flour, till it was all leavened” (Matt. 13:33). In both cases the “leaven” in mind is a set of assumptions about life, a worldview, an understanding of reality, an approach to life. 

Leaven is a good image. It works silently and gradually, and it affects the whole loaf. Whether through the promotion of arrogance or the Kingdom of God, leaven has this property: It spreads unnoticed, but it ultimately affects everything.  The leaven of the Pharisees was religious pride, but the leaven of God’s kingdom is humility. 

However, the leaven of the gospel is at a disadvantage. The leaven of the Pharisees is natural to the flesh.  Therefore, the leaven of the Pharisees spreads easily––without resistance. It is welcomed by the loaf. By contrast, the leaven of God’s Kingdom is foreign to the loaf. The loaf must be changed by the miracle of new birth before God’s leaven can do its wonderful work. 

Because the leaven of the Pharisees is natural to the loaf, it must be continually and aggressively displaced by the gospel. This means that assuming the gospel will be fatal, or that neglecting the gospel will be terminal. To counteract the leaven of the Pharisees, we  must preach the gospel to our selves daily. We must preach the gospel to our congregations repetitively. If we don’t the leaven of the Pharisees will overcome it.