The Potency of Sin and the Purity of Christ
Introduction: A Tolerant Church is a Dying Church
The Corinthian church was a mess, but they were a proud mess. They were gifted, they were eloquent, they were sophisticated, and they were congratulating themselves on their broad-minded tolerance. As we saw in the first part of this chapter, they had a man in their congregation who was engaged in a particularly grotesque form of sexual immorality, and instead of grieving, they were puffed up. They likely thought of themselves as the advanced party, the enlightened ones who were above such petty moral judgments. They were the original "love wins" crowd.
Paul's response to this is not a gentle suggestion. It is a thunderclap of apostolic authority. He has told them to gather together and to deliver this man over to Satan for the destruction of his flesh, so that his spirit might be saved. This is not vindictive; it is redemptive medicine. But Paul is not just concerned for the man's soul; he is concerned for the integrity and life of the entire church. The Corinthians' boasting was not just inappropriate; it was lethally dangerous. They were celebrating a cancer in their own body. They were proud of the poison in their own well.
In our passage today, Paul moves from the specific case to the general principle. He uses a powerful, everyday metaphor to show them the spiritual reality of what they are doing. Sin is not a private affair. It is never "just between me and God" when you are part of the covenant community. Sin, particularly unrepentant, public sin that is tolerated by the church, is like leaven. It is potent, it is pervasive, and it will inevitably work its way through the entire lump. A little bit of compromise, a little bit of pride, a little bit of looking the other way, and soon the whole church is affected. Purity is not an optional extra for the super-spiritual; it is a matter of life and death for the body of Christ.
The Text
Your boasting is not good. Do you not know that a little leaven leavens the whole lump? Clean out the old leaven so that you may be a new lump, just as you are in fact unleavened. For Christ, our Passover lamb, also was sacrificed. Therefore let us celebrate the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.
(1 Corinthians 5:6-8 LSB)
The Contagion of Sin (v. 6)
Paul begins by directly confronting their sinful pride.
"Your boasting is not good. Do you not know that a little leaven leavens the whole lump?" (1 Corinthians 5:6)
Their "boasting" or "glorying" was entirely misplaced. They were proud of what should have been a cause for deep corporate grief and repentance. This is a profound spiritual blindness. When a church can look at flagrant sin in its midst and call it "grace" or "tolerance," it has lost its way entirely. It is like a doctor boasting about the interesting colors in a gangrenous wound. It is not good.
Paul then asks a rhetorical question to drive home the danger: "Do you not know that a little leaven leavens the whole lump?" This was a common proverb, a bit of kitchen wisdom that everyone would have understood. Leaven, or yeast, is a powerful agent. You only need a small amount to affect the entire batch of dough. It works silently, invisibly at first, but its effect is total. In Scripture, leaven is almost always a symbol of corrupting influence. Jesus warned his disciples to beware the leaven of the Pharisees and Sadducees, which was their false doctrine and hypocrisy (Matt. 16:6).
The principle is this: tolerated sin is corporate sin. The sin of one member, when it is known and not addressed, becomes the sin of the whole church. Why? Because the failure to discipline is itself a sin. It is the sin of compromise, the sin of cowardice, the sin of valuing a false peace over biblical purity. It communicates to everyone that this particular sin is not actually a big deal to God, and that holiness is not actually required among His people. This attitude is the "leaven." It starts with one case, but the principle of compromise spreads. If we tolerate this, why not that? And if that, why not the next thing? Soon, the entire church is puffed up, not with the Holy Spirit, but with the leaven of worldliness.
Cleaned Out by the Cross (v. 7)
The solution is not to manage the leaven, but to eradicate it. Paul grounds this command in the finished work of Christ.
"Clean out the old leaven so that you may be a new lump, just as you are in fact unleavened. For Christ, our Passover lamb, also was sacrificed." (1 Corinthians 5:7)
The command is to "clean out the old leaven." This is a direct allusion to the Feast of Unleavened Bread, which immediately followed the Passover. For seven days, the Israelites were commanded to eat only unleavened bread and to remove every trace of leaven from their houses (Ex. 12:15). This was a powerful object lesson. The leaven represented the corruption of Egypt, the old life of bondage they were leaving behind. To purge the leaven was to make a clean break with the past.
Paul applies this directly to the church. He says, "clean out the old leaven, so that you may be a new lump." This is the work of sanctification. But notice the beautiful gospel logic that follows. He says you must do this "just as you are in fact unleavened." This is the glorious indicative and imperative of the Christian life. You must become what you already are. In Christ, your legal standing before God is "unleavened." You are declared righteous. You are a new creation. The old leaven of sin and guilt has been judicially removed. Now, you are commanded to live out that reality in practice. You are to work out the salvation that God has worked in. The practice of church discipline is simply the church acting like what it is: a holy people, set apart for God.
And what is the basis for this new, unleavened identity? "For Christ, our Passover lamb, also was sacrificed." This is the heart of the gospel. The Passover lamb was slain, and its blood was applied to the doorposts, so that the angel of death would pass over the houses of the Israelites. Jesus is the fulfillment of this type. He is the Lamb of God, slain for us. His sacrifice has dealt with the wrath of God. His blood has cleansed us. The Exodus was the great redemptive event of the Old Testament; the Cross is the great redemptive event of all history. Because our Passover Lamb has been slain, we have been delivered from the bondage of sin. Therefore, we must no longer live as though we are still in Egypt.
Keeping the Feast (v. 8)
Paul concludes by describing what this new life, this perpetual festival, looks like.
"Therefore let us celebrate the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth." (1 Corinthians 5:8)
Because Christ has been sacrificed, the entire Christian life is a festival. We are to "celebrate the feast." This is not a once-a-year event; it is a continual state of being. We live in the reality of redemption. We are a festival people, a joyful people, a celebrating people. But this celebration has a particular character. It must be consistent with the sacrifice that made it possible.
We are not to keep the feast "with old leaven." This is the leaven of our former life, the patterns of sin we were saved out of. Paul then specifies this leaven as "the leaven of malice and wickedness." Malice (kakia) is the desire to injure another. It is ill-will, spite, and malevolence. Wickedness (poneria) is active, deliberate evil. It is the character of one who loves what is evil and seeks to do it. This is the leaven of Egypt. This is the leaven that was present in the Corinthian church, both in the incestuous man and in the arrogant tolerance of the congregation. You cannot celebrate the grace of God while simultaneously coddling the very things from which He saved you.
Instead, we are to feast "with the unleavened bread of sincerity and truth." Sincerity here means purity of motive, without hypocrisy. It is an unmixed, unadulterated integrity. Truth is not just doctrinal accuracy, but a life that corresponds to reality as God has defined it. It is living in accordance with the Word of God. Sincerity and truth are the bread of the kingdom. This is what our feast consists of. This is the atmosphere of a healthy church. It is a place where sin is taken seriously precisely because grace is treasured so highly. It is a place where people are honest with one another, where truth is spoken in love, and where everyone is committed to walking in the light, as He is in the light.
Conclusion: The Joy of a Clean House
The modern church is terrified of church discipline. We have been catechized by the world to believe that the highest virtue is tolerance and the greatest sin is judgment. But Paul shows us that true love for God, true love for the sinner, and true love for the church demands that we take sin seriously. A church that refuses to discipline is a church that has forgotten the meaning of the cross. If sin is no big deal, then Christ's death was a tragic overreaction.
But because Christ our Passover has been sacrificed, sin is a massive deal. It is what nailed Him to the tree. And because He has been sacrificed, our sin has been dealt with decisively. We are now unleavened. We are a new lump. Our task, as a covenant community, is to live this out. It means having the courage to "clean out the old leaven." It means confronting sin, calling for repentance, and, when necessary, removing the unrepentant from our fellowship, always with the goal of restoration.
This is not a grim, legalistic duty. It is the joyful work of keeping our house clean for the festival. It is how we protect the flock from the leaven of malice and wickedness. It is how we ensure that our fellowship is characterized by the unleavened bread of sincerity and truth. A church that practices biblical discipline is a church that is safe for sinners who want to repent, and dangerous for those who want to persist in their sin. And that is a church that truly understands the joy of the feast.