Churches have many ways to deal with sin in the body. Sadly, the most common way to handle sin in the modern evangelical church is ignoring it. However, if we don’t deal with sin in the church biblically, we neglect something critical in God’s Word, imperiling the transgressor.

One tool God uses to preserve His people is faithful, biblical church discipline. Churches are called to exercise discipline and remove members who persist in unrepentant sin for the good of the sinner. The goal is redemptive, so when Christ comes, those formerly in sin will be saved.

There’s a second reason why churches should exercise discipline by removing unrepentant sinners from membership, and that is to preserve the church’s purity (1 Corinthians 5:6-8). Paul was concerned for the holiness of God’s people. He understood we commonly underestimate the damage unchecked sin or false teaching does to a church. So, in this passage, Paul gives three truths to encourage Christians to vigilantly guard the purity of the church.

First, we must understand that sin contaminates God’s people (verse 6).

This foundational principle helps us see the seriousness of allowing sin to go unchecked among God’s people. We so easily can underestimate the gravity of sin – especially within the church. It might seem like some people make significant positive contributions to the life of the church and removing them would do more harm than good. Yet here, Paul warns that whatever good someone might do in the church through the exercise of their gifts or financial giving will result in a net loss if their sin is allowed to remain within the body of Christ.

Paul again reminds the Corinthians that their boasting is not good. Rather than boasting about their spirituality, they should have been demonstrating how spiritual they were by confronting sin in the church. To humble their pride, Paul asks them a cutting question with a proverbial statement about leaven: “Do you not know?” For all the complicated things they claimed to know, and for all the world-class teachers they followed, the Corinthians couldn’t even comprehend a simple truth, that a little leaven leavens the whole lump of dough.

Leaven was common in the ancient world and was a normal part of the baking process. Because of the penetrating power of such a small amount of leaven, it became a proverb to speak of the pervasive, penetrating power of various objects. This proverb could be used both positively and negatively. For example, Jesus used this same concept positively (Matthew 13:33). Leaven is used in this parable to speak of the pervasive power of God’s kingdom, which would start small and grow to expand.

Most of the time, however, leaven is used in the New Testament as a negative influence. Jesus often used leaven to refer to the wickedness of the Jewish religious leaders. He instructed His disciples to look after their own hearts, and not to be hard-hearted like Herod and the Pharisees (Mark 8:17). Jesus also warns that false teaching is like leaven, spreading to corrupt countless people (Matthew 16:12). Additionally, Jesus commands His disciples to beware of the danger hypocrisy presents to His followers (Luke 12:1).

When we look at Paul’s use of leaven in the context of this passage, we must conclude he is using leaven as a symbol for something evil and dangerous. What, then, does Paul have in mind as the leaven? Here’s the answer: when the church does everything it is supposed to do, except deal with sin, it is play-acting and hypocritical. A little sin left unchecked will eventually kill an entire local church.

Second, we should understand that the Savior cleansed God’s people (verse 7).

When sin has its way in the church, Christians forget the reality of Christ’s sacrifice. Paul commands the Corinthians to remove the old leaven so they might be a new lump of dough. Some people will recognize their sins, repent, and move forward in purity; while others, tragically, will stubbornly remain in sin and be removed from the local church.

What’s fascinating, however, about Christian ethics is that every imperative is predicated on an indicative. Paul reminds the Corinthians that they already are unleavened. These statements relate to the old life before Christ and the new life in Christ. Paul is not merely saying they must get rid of sin (as if sin is an isolated act of disobedience); rather, he is stating that they must stop living like people from this present age.

Even as Christians, it’s so easy to live for now, the applause of men, and status and renown. We often think that if we make it here, we’ve made it in the new creation. Everything, though, about heaven is opposed to the present-world system. This truth is why Jesus says, “Woe to you who are rich, well-fed, and well-spoken of by the world!” (Luke 6:24-26) Worldly values, must go, because sin has no place in the new creation.

Remember that Passover was the feast God instituted when He prepared to bring the final plague on the Egyptians and deliver Israel from slavery. This feast was a foreshadowing of what Christ would do for His people. Paul says, then, that we know we are an unleavened lump of dough because the new covenant Passover lamb has been sacrificed. Therefore, we should stop living like we are still part of the old creation.

Finally, we need to understand that sanctification should characterize God’s people (verse 8).

The Christian life is a perpetual Passover festival. It is a celebration that the new has broken into the old, transforming us in its wake. Believers rejoice that Christ has been sacrificed for our sins and that He has set us free from bondage to impurity.

Now, Paul does not mean that we celebrate the old covenant Passover feast under the Law. Some believe we must continue to mark all the old covenant feasts and sabbaths, but Paul is quite clear that we are now in the new creation – and the old covenant festivals are obsolete. Also, we don’t celebrate the festival by indulging sin. Sin should not define the believer.

Here’s what Paul does mean, though. We celebrate with the unleavened bread of sincerity – the opposite of hypocrisy. Christianity is never about pretending to be something we aren’t to gain a status we don’t have. Instead, Christianity is about learning to be what we truly are because of a status we already have. Believers want to manifest who we really are in Christ, so the world sees the in-breaking of the new creation in the church.

Then, we celebrate with the unleavened bread of the truth, which refers most directly to the truth of God’s Word. The Lord wants the truth to form, shape, direct, guide, and control us (Psalm 51:6). So, we celebrate the festival, not merely intellectually or theologically, but practically, living out the truth of God’s Word in sincere truth.

John MacArthur wrote, “Those two words are synonyms for purity, the purity of the cleansed new life in Jesus Christ.” Believers must also guard that purity in the church when it is threatened by someone in the body living a life of unrepentant sin.

So, church discipline is for the purity of the church, which is always compromised when sin is unchecked in the body of Christ. The glorious news of the gospel, however, is that Christ our Passover has been sacrificed, so those who trust in Him are cleansed of sin, set free from slavery, and made new creatures. Our job – and privilege – as the church is to manifest to the watching world what this new creation will be like.