“Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.” (Matthew 16:6 KJV)
Leaven? As in yeast or some other substance that ferments an entire piece of dough? How would the leaven of the Pharisees (or that of Herod – see Mark 8:15) be bad? Luke 12:1 connects this leaven with hypocrisy or acting. 1 Corinthians 5:8 is similar in that it connects leaven with malice and wickedness. Yet Matthew 13:33 and Luke 13:21 have a sharp contrast with this. They portray leaven as an example of the kingdom of heaven like something that is hidden within until it was dispersed throughout the dough. Is there a difference between leavens that goes beyond simply leavened verses unleavened? Leaven appears to be a handy illustration for something that overruns rapidly and thoroughly with only a very small quantity at initialization. There seems to be some contention as to whether this overrun is an infestation or a cure. As with many things, I imagine it has to do with the heart of the matter.
Consider for a moment the significance of this difference. Have you ever been in a conversation where someone slipped an unnecessary innuendo in and it effectively soured the whole discussion? Or perhaps another person spoke a timely word that had meaning and truth to it and it had an obvious effect of salvaging the whole talk? Perhaps a show you were watching had unnecessary scenes in it and it tainted the whole story. Or another character stepped in and revealed a reason to press on, a life worth reaching for, or an understanding that illuminated the whole mystery. Consider the practical effects of a bribe verses transparent honesty. An insincere compliment verses duly earned respect. An opportunity at dishonest gain verses the chance to step in and insure justice. Leaven infects or cures very rapidly and in all parts of the body.
In either case, leaven is not something to co-exist and have no effect on. It transforms the bread and cases the whole loaf to rise. Leaven may be a like a virus or an antidote, but not likely a balancing agent. Hebrews 4:12 suggests that the Word of God is powerful. It does not obtain that power by maintaining. Rather things maintain because God's Word upholds them. Stepping into a situation with light will rid the room of darkness. The power Jesus uses steps into a location with the intention of cleaning it. He is not afraid of touching something for fear of infection.
Consider for a moment a possible context that Jesus may have been thinking about in reflecting on the feeding of thousands. In preparing a correlation for his disciples would it not make sense to counter the leaven of the Pharisees with how the kingdom of heaven spreads? It obviously went well beyond having or not having bread. It goes to the heart of what genuine faith in God really does. If anything, the suggestion in 1 Corinthians 5:8 of maintaining unleavened bread altogether would be an acknowledgment that we need no leaven of our own. The leaven that we need to allow to work it's way through us unto completion would be those things of Christ which completely remake us. Those things which give rise and substance to someone who is not trying to raise themselves up in pride and the temptation to increase for ourselves. Our reliance should increase in Jesus not decrease.
“And as they did eat, Jesus took bread, and blessed, and brake it, and gave to them, and said, Take, eat: this is my body.” (Mark 14:22 KJV)