Christ, Our Passover Lamb

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. Let us therefore celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth. (1 Corinthians 5:7-8 ESV)

In First Corinthians chapter 5, Paul has just told the Corinthians that he, by apostolic authority was excommunicating the adulterer in their midst. Furthermore, Paul explained that they as a congregation should have acted already. He gave two reasons in verses 5:7-8, which I quoted above, for why they needed to excommunicate the specified member. Let us break down the passage piece by piece.

Cleanse out the old leaven that you may be a new lump, (1 Corinthians 5:7a)

The first reason for the excommunication is the Christian community has to be free from the impurities of sin and contention. The saying is the same as "One bad apple spoils the bunch." This one believer was corrupting the congregation and spoiling their testimony in the community. Fee made the following observations on the first reason.

What is in view is not “yeast” (as in the NIV), which was not plentiful in antiquity, and which in any case is fresh and wholesome. “Leaven” was not so. It consisted of keeping back a “little” portion of last week’s dough, allowing it to ferment, then adding it to this week’s dough, which in turn was thoroughly fermented to give it lightness (=sourdough bread). Although the OT does not expressly so specify, the Feast of Unleavened Bread, as well as being a religious celebration, was probably a health provision. Because of the fermentation process, which week after week increased the dangers of infection, the Israelites were commanded once a year to purge their homes of all leaven (Exod. 12:14-20). During the Feast they would bake only unleavened bread, from which dough they would then start up the process again after the Feast. Thus in the NT leaven became a symbol of the process by which an evil spreads insidiously in a community until the whole has been infected by it (cf. Mark 8:15). (Fee, The First Epistle to the Corinthians (New International Commentary on the New Testament) , p. 216)

However, as you see in the next part of the passage, Paul reminds the Corinthians that due to Christ's death and sacrifice, they are already pure both individually and corporately in God's eyes. They need to live as God sees them already in Christ.

as you really are unleavened. (1 Corinthians 5:7b)

Fee explains further.

In so applying the imagery, however, Paul expresses himself in a way that is foreign to his own theology; so he immediately qualifies it with “even as you really are.” “As always in Paul, the imperative, even though it must be obeyed, cannot be turned into a piece of legal material, obedience to which gives favor with God. Right at the point where the imperative sounds as if it comes, first (“Get rid of the old so that you may be new”), he reminds them that what they must become is what they already are by the grace of God. (Fee, p. 218-219)

The second reason for why the Corinthians congregation should have acted sooner in punishment is in the third part of the passage.

For Christ, our Passover lamb, has been sacrificed. Let us therefore celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth. (1 Corinthians 5:7-8 ESV)

Charles Hodge, in his commentary on Corinthians, makes the dramatic connection between the quaint saying "A little leaven leavens the whole lump" to an explanation of Christ's death on the cross as illustrated in the Jewish Passover.

This is a second reason why they should be pure; for Christ our passover is slain for us. Is slain; rather, is sacrificed as θυω means to kill and offer in sacrifice or to slay as a victim. When the paschal lamb was slain the Hebrews were required to purge out all leaven from their houses Ex 12, 15. The death of Christ imposes a similar obligation on us to purge out the leaven of sin. Christ is our passover not because he was slain on the day on which the paschal lamb was offered, but because he does for us what the paschal lamb did for the Hebrews. As the blood of that lamb sprinkled on the door posts secured exemption from the stroke of the destroying angel, so the blood of Christ secures exemption from the stroke of divine justice. Christ was slain for us in the same sense that the passover was slain for the Hebrews. It was a vicarious death. As Christ died to redeem us from all iniquity, it is not only contrary to the design of his death but a proof that we are not interested in its benefits, if we live in sin. Our Passover, viz., Christ. (Hodge,1 & 2 Corinthians (Geneva Series of Commentaries) ,p. 87)

If the Church, the body of Christ, treats sin lightly or disregards the leaven in its midst, it cheapens what Christ has done for it. We must purify ourselves of the leaven of sin and contention among us so we can celebrate Christ's death in purity and sincerity.