“Beware of the leaven of the Pharisees,” Jesus warned his followers – a reference sufficiently obscure that even his closest disciples missed the point. Only belatedly did they realize Jesus was warning them against the teachings of a religious group he had tangled with numerous times over the finer points of faith and doctrine. The Pharisees are generally portrayed in the New Testament as a bunch of nitpickers, a characterization that some modern scholars view as unduly harsh. The Pharisees are no longer around to defend themselves, but the spirit of Pharisaism clearly lives on among hardcore believers of every faith – not the least among Christians themselves. These are the folks who delight in doing everything by the book, whether on matters of doctrine, religious practice or personal conduct.
Leaven has special significance in Judaism because of the dietary laws connected to the Passover celebration. The Festival of Unleavened Bread, as it is also called, marks the deliverance of the Hebrew people from slavery in Egypt. According to the Book of Exodus, the Hebrews left Egypt so quickly they had no time to leaven their bread. Their deliverance from bondage is now commemorated by eating only unleavened bread for seven days. Before the start of Passover, observant Jews gather up all bread products made with yeast in their household and burn them. Their homes are thoroughly cleaned, and kitchen utensils are scrubbed to remove all traces. This may explain why St. Paul, himself a Pharisee, once made reference to this practice in exhorting believers to “cleanse out the old leaven that you may be a new lump.”
The thing to remember about leaven is that a little goes a long way, or as Paul expressed it, “A little leaven leavens the whole lump.” This was the point of Jesus’ parable in which he compared the kingdom of heaven to a woman hiding leaven in three measures of flour. Unfortunately, the same principle applies when you are talking about the leaven of the Pharisees. This is why the prophets and visionaries of every religious tradition are so quickly shunted aside by priests and theologians. We should keep in mind that leaven has no nutritional value in itself; it may cause the bread to rise but it’s just hot air.
1 Corinthians 5:6-7