In Deuteronomy 16, God tells the Israelites how to observe the Passover.

Everything about this festival was meant to call to mind the events of the great exodus from Egypt. There was even a lesson in the bread that they ate. For God said, “You shall eat no leavened bread with the lamb; seven days you shall eat it with unleavened bread…the bread of affliction” (v. 3). That humble bread was of great importance. So much so, that Passover sometimes went by a different name: it was called “the Feast of Unleavened Bread.” 

Unleavened bread is hard to chew, tough and dense. Why eat these sorry loaves? There’s at least two reasons.

First, see how God calls it “the bread of affliction.” Sometimes we talk about “comfort food,” meaning food that makes us feel good inside. It might be spaghetti or lamb stew with flatbread—stuff that brings back good memories of home and family. The unleavened bread did the opposite: it reminded them of Egypt’s hardships and misery. Gnawing on “the bread of affliction,” the Israelites had to think about how they used to be lacking in every comfort, and how God delivered them.

Moses gives a second reason for the bread: because “you came out of the land of Egypt in haste” (v 3). When you’re baking bread, you have to wait an hour or two for the yeast to do its work in the dough. But when Pharaoh finally relented, the Israelites had to leave at once—even if they were in the middle of something, like baking bread. So the unleavened bread also reminded them of that frantic but wonderful night when God brought them out.

And God took this aspect of the meal seriously: “No leaven shall be seen with you in all your territory for seven days” (v. 4). It wasn’t enough that the Israelites eat bread without yeast at Passover; there wasn’t allowed to be any yeast, in any of their homes, the whole time of the festival!

Bible explainers aren’t sure why God commanded this total ban. Some say that leavened bread is moister and would quickly go bad; covered with those little spots of blue mold, the bread would be impure, and impurity wasn’t right for a people celebrating a holy festival.

Being yeast-free could be about avoiding moldy bread, but there’s probably more to it. We just spoke of purity, and that’s probably still the chief concern. In Bible times, the leavening process—when you add yeast to dough—wasn’t considered entirely clean. For yeast is a kind of fungus, whose microorganisms will spread in a lump of dough. As it reacts with the other ingredients, it forms the little air pockets that make bread so soft. Maybe you’ve seen a starter jar for sourdough bread: a bubbling, growing, mush of yeast and bacteria. Looks terrible, but it makes delicious bread.

For the Israelites’ regular diet, leavened bread was acceptable. But it wasn’t suitable for an occasion like Passover. This is why God instructs, “Do not offer the blood of a sacrifice to me along with anything containing yeast” (Exod 23:18). No yeast with the sacrifices! And for the Passover week, the same rule applied: No yeast!

Because of this, a custom developed. Before preparing the Passover, the Israelites would sweep clean the whole house, top to bottom, just to be sure that no yeast was left over. Even the little crumbs from leavened bread were removed. This reminded them of the need for complete holiness. Let there be no infecting evil among you. Don’t allow any wicked mold to grow on your heart. Be dedicated to God with uncompromised devotion.

In the New Testament, we still come across this warning against “spiritual yeast.” “Be careful,” Jesus said, “Watch out for the yeast of the Pharisees” (Mark 8:15). Their teaching could corrupt people with its legalism and empty religion. Beware of that dangerous yeast, before it sinks in!

Has this changed? The holy God still calls us to be pure, just as He is pure. For instance, Paul reproves the Corinthians, “Do you not know that a little leaven leavens the whole lump?” (1 Cor 5:6). He uses leaven to picture how sin can affect us so deeply, and affect those around us. He urges the Corinthians to discipline the unruly person, before more people in the church are corrupted. 

Because just like a bit of yeast in dough will gradually work its way through, so will sin. Sin is like a stubborn fungus, a fermenting bacteria: sin can multiply in the church, and it can multiply in our hearts. When we leave sin alone, when we let it be, it’ll never remain as is.

For instance, when we’ve become slack in our personal devotions, we’ve probably also started to accept other little sins in our life—not being totally honest with our spouse, or getting lazy in other areas of life, like our daily work.

Or maybe we dabble in a sinful pleasure once or twice—we look at porn, smoke some weed—and this little thing grows into a killer habit, an addiction we can hardly break.

Perhaps the bitterness you hold toward a family member starts to extend toward people in your church too, then people at work—and after a while, you realize you’ve become a bitter person. Sin has grown.

Like mold, sin spreads—it touches new parts of our life, even areas previously fine.

God’s solution: “Cleanse out the old leaven that you may be a new lump, as you really are unleavened!” (5:7). Sweep your heart clean, top to bottom. Get rid of every offending crumb of sin before it causes more harm. Pray for God’s help to flee every impurity, to be rid of all envy. Don’t give a foothold to your lust. Destroy that pride. Deal with your anger.

Then the marvelous reason: “For Christ, our Passover lamb, has been sacrificed” (5:7). Jesus fulfilled the ancient Passover; He took those old symbols of wine and bread and gave them a powerful new meaning.

Whenever we celebrate communion, we remember how Christ saved us. The Passover Lamb was slaughtered, his blood poured out, to redeem us forever. The wine and bread of communion are the greatest “comfort food,” assuring us of our only comfort in life and death.

The Passover is fulfilled, but Christ still calls us to be unleavened. It’s not about the bread on the communion table. It’s about us. Will I be pure in heart for my Saviour? Will I be devoted in every area of my life that I can think of? Will I strive to be 100% yeast free?

Get rid of the old yeast, says the Holy Spirit: “Let us celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth” (5:8). As a believer, you get to eat the bread of Christ—and to let his grace move you to a life of deep holiness, sincerity and truth.

Put away the old yeast and let it infect you no more. For Christ, our Passover Lamb, has been sacrificed.