Question: "What does it mean that a little leaven leavens the whole lump (Galatians 5:9)?"

Answer: A little leaven leavens the whole lump is a metaphor the apostle Paul uses to compare the effects of false teaching in the church to the results of yeast in bread dough (Galatians 5:9). Just as a small amount of yeast will make a whole loaf of bread rise, a little bit of legalistic teaching will quickly spread, infiltrating the hearts and minds of individual believers until the entire church is contaminated.

Leaven is any substance (like yeast) used to produce fermentation in dough. It is the main ingredient that causes bread to rise in preparation for baking. The “whole lump” in Galatians 5:9 refers to an entire batch of dough and in Paul’s analogy denotes the whole congregation of believers.

In Galatians 5:1–6, Paul stresses that Christ, by God’s grace and through the inner working of the Holy Spirit, has set believers free from slavery to the outward control of the law. Then he begins to list the destructive consequences of returning to a legalistic bondage to the law. One adverse outcome is stunted spiritual growth: “You were running well. Who hindered you from obeying the truth? This persuasion is not from him who calls you. A little leaven leavens the whole lump. I have confidence in the Lord that you will take no other view, and the one who is troubling you will bear the penalty, whoever he is” (Galatians 5:7–10, ESV).

Employing one of his favorite comparisons, Paul likens the Christian life to a race. The Galatians were excelling in the race until false teachers cut into their spiritual marathon. They set up obstacles of legalism, confusing the believers and hindering their spiritual development. The stumbling Galatians had stopped obeying the truth as the influence of bad company corrupted their good character (1 Corinthians 15:33).

Paul then engages his yeast comparison, emphasizing that a little bit of legalism in the church—like leaven in a batch of dough—goes a long way. “Leaven” here symbolizes wrong teaching that destroys true Christian freedom. Paul quickly communicates his trust in the Lord to keep the Galatians on the track of truth and warns that God will judge the false teachers who had been tripping them up.

Paul uses this same yeast metaphor with the church in Corinth: “Your boasting is not good. Do you not know that a little leaven leavens the whole lump? Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our Passover lamb, has been sacrificed” (1 Corinthians 5:6–7, ESV).

Here, “leaven” represents sin, and precisely the sin of pride (1 Corinthians 5:2). Paul wants to protect the church from the disastrous consequences of moral corruption. Their arrogant attitude of tolerating an appalling sin in the church posed a severe threat. Allowing one believer to continue unchecked in a blatant transgression would have a devastating impact on the entire church. Paul asks, “Don’t you realize that this sin is like a little yeast that spreads through the whole batch of dough?” (1 Corinthians 5:6, NLT).

Paul is adamant. The church must deal with the person’s sin. A single member’s sin affects the entire body because we are all collective parts of one whole (1 Corinthians 12:12–26). The church should heal, restore, and keep the body as one pure and moral community of believers because it lives and moves and has its being in Christ (Acts 17:28; Romans 12:5). Paul explains, “Then you will be like a fresh batch of dough made without yeast, which is what you really are” (1 Corinthians 5:7, NLT).

Paul’s metaphor of a little leaven leavens the whole lump is rooted in the significance of Christ’s sacrifice and directly tied to the Passover. Paul concludes, “For Christ, our Passover lamb, has been sacrificed” (1 Corinthians 5:7). Jesus is our Passover Lamb of God (John 1:29; Revelation 13:8). When Christ died on the cross, His blood was spilled to protect us from God’s wrath, just as the blood spread over the doorframes of the Hebrews’ homes protected them in Egypt (Exodus 12:7).

As part of the Passover commemoration, the ancient Israelites were forbidden to bake or eat leavened bread or even have leaven in their homes. This tradition was observed in remembrance of Israel’s hurried exodus from Egypt, which gave no time for preparing leavened bread (Exodus 12:33–34, 39). Knowing Christ is our Passover, Paul urges believers to remember His sacrifice by removing the “old leaven” of sin from our individual lives and our congregations.

Jesus also used the word leaven to describe the corrupt teachings of the Sadducees and Pharisees (Matthew 16:6, 11–12) and Herod (Mark 8:15). Like leaven that works its way through dough, spreading out until its effects are manifest in the entire batch, Jesus warned that the ideas of Herod and the religious leaders were steadily permeating the people’s thinking. Even a little leaven leavens the whole lump of dough just as a tiny bit of sin, or just a small amount of harmful teaching, has a widespread corrupting influence on the minds and hearts of people.

Only once in the New Testament is leaven used as a positive metaphor. Jesus said, “The kingdom of heaven is like leaven” (Matthew 13:33, ESV; Luke 13:20–21) to illustrate the ever-increasing, pervasive influence of God’s kingdom in the world.