Pride puffs us up. That is a vital lesson of leavening that we are all familiar with. We talk about people having a big head, thinking they are big stuff. Vanity and arrogance truly are dangerous to our spiritual health. They can lead us to cut ourselves off from God, leading to spiritual death!

But the puffed up stage of leavening is not immediate. It takes time for tiny yeast microorganisms to multiply and spread. By the time swelling comes, the process—the infection—is well along. Paul wrote to the Corinthians: "Do you not know that a little leaven leavens the whole lump? Therefore purge out the old leaven, that you may be a new lump" (1 Corinthians 5:6-7). They were exposing themselves to infection, instead of quarantining the one who was spreading wrong attitudes.

Think of leavening as an analogy of disease cells in the body that must be killed or removed. If you get to them quickly, then you can prevent further damage. But unchecked, the infection grows out of control and can lead to our death.

Biological and Chemical Warfare

For a week each year we can think of leavening as a weapon of Satan. The leavening we avoid comes in two types: biological (yeast) and chemical (baking powder and baking soda). Biological and chemical weapons are among the most feared types of warfare today. And so their spiritual counterpoints should be to the Christian.

Some of the gases that have been used in chemical war can incapacitate a man in concentrations as little as one part in 10 million. How much sin can we touch and say, "that won't hurt me"? The only true protection is to get away from the cause.

God gives us the power, through His Holy Spirit, to address the cause of the infection, the sin. "For the weapons of our warfare are not carnal but mighty in God for pulling down strongholds, casting down arguments and every high thing that exalts itself against the knowledge of God, bringing every thought into captivity to the obedience of Christ" (2 Corinthians 10:4-5).

Replacing the Leaven

The old leaven must be put out and replaced by the Holy Spirit. You can't get rid of poisoned air in your lungs without taking in good air to replace it. If a new man is not created after the old man is put away in baptism, the old man simply rises to live again.

Sin is a dangerous infection to be avoided at all costs. As you set aside the bread, the croutons—the leavening—this year, think about putting out the infection of sin. As we eat the unleavened bread, we can be reminded we are not just putting sin out, but God is putting His nature in.