What does it mean to purge out the old leaven (1 Corinthians 5:7)?

In 1 Corinthians 5:7, the apostle Paul writes, “Purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us” (NKJV). Paul uses leaven, or yeast, as a metaphor for sin in the church. Sin must be purged from the congregation because God has called us to holiness.

The specific circumstance requiring the purging of the “old leaven” was a case of sexual immorality in the Corinthian church. Paul opens the chapter by saying, “It is actually reported that there is sexual immorality among you . . . that a man has his father’s wife!” (1 Corinthians 5:1, NKJV). This situation was out of bounds, even by pagan standards. A man living with his stepmother was engaging in flagrant immorality, and it was no secret in the community. The believers in Corinth should have been ashamed of themselves for tolerating such behavior in their midst; instead, they treated the matter lightly. Paul rebukes their lenience and calls them to excommunicate the offender: “Deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus” (1 Corinthians 5:5, NKJV). The “leaven” of immorality should be removed to protect the integrity and purity of the church.

In the same context, Paul warns of the insidious nature of leaven. Yeast pervades whatever batch of dough it’s in: “Do you not know that a little leaven leavens the whole lump?” he asks (1 Corinthians 5:6, NKJV; cf. Galatians 5:9). Tolerating unrepentant sin can corrupt the entire local body. The Corinthians must “purge out the old leaven” before its effects spread and others are corrupted.

The Greek verb translated as “purge out” indicates a decisive and immediate action. Paul commands the Corinthians to take swift action against the sexual immorality. It is not a suggestion but an urgent demand to protect the sanctity of God’s household.

Paul mentions Passover and applies the rituals associated with that feast to the need for holiness in the church. During Passover and the Feast of Unleavened Bread, all leaven was carefully removed from every house as a sign of being separated unto God (see Exodus 12:15; Deuteronomy 16:3–4). Passover itself signified freedom from slavery in Egypt and the Israelites’ new life with God. In Paul’s metaphor, the “old leaven” is part of the old, sinful life. Christians have been set free from the slavery of sin and should no longer be dabbling in the old ways.

“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 5:7, ESV). The sacrifice has been made—Christ, the Lamb of God. The lump [of dough] has been purified—the church has been forgiven from sin. We are unleavened—God has sanctified us. So, why is the church allowing sin to continue in their ranks?

We have a new identity in Christ. We have been cleansed and set apart—we are a new batch of dough. We must beware the contaminating influence of spiritual leaven (cf. Mark 8:15).

Sin in the church must be dealt with, and Jesus gave us the blueprint to follow (Matthew 18:15–18). Church discipline is never easy, but sometimes it’s necessary to maintain the spiritual and moral integrity of the church. The goal is the restoration of the sinner, and we have instructions concerning that in 2 Corinthians 2:5–11.