The Power to Change
1 Corinthians 5 is a hard chapter; Paul is abrading the Corinthian church for allowing a man to hang around who took his father's wife. Paul's larger point is clear - don't tolerate what even non-Christians don't tolerate (v. 1). But in verses 6-8 Paul pictures crucial truths for us, for growth, change and sanity:
First, that grave danger underlies all boasting. Verse 6 - boasting is not good, not in a moralistic sense, but because the pride that undergirds it blinds us to the true dangers of sin. Part of the trickery of sin is to keep our eyes on the lure, and not the lethal precipice we are being groomed to approach. Sin's real power is the power of a lie. Boasting reveals a pride that has already bought into sin's lie.
Second, the lie has to do with our identity, and the power to live in it. Paul uses Old Testament imagery here: the "old leaven" was a small lump of old dough that would be placed in the new dough, to begin the fermentation process in the new dough. But old leaven was dangerous - it could spoil, infect and sicken. So Paul says, "get this guy out of here".
Now catch the reason, verse 7: because you, Christians, "really are" unleavened - you are pure. The question is one of identity. This is not you, he says, nor do you need this. You are pure, and already alive.
But how do we sinners sincerely believe Paul? "For Christ, our Passover lamb, has been sacrificed." We who believe on Christ are cleansed by his blood, united to him in his purity.
Therefore, we "celebrate the festival" - not the literal, Old Testament Passover festival, but our Passover lamb; - Christ. Here we land at ground zero for growth, change, and sanity. We gain the courageous sanity necessary to live out our new identity in Christ not by keeping the rules, nor by pretending, but by celebration - celebrating within ourselves and with each other all that God is for us in Christ.
Note well: this is not just a looking back to the cross. The cross is proof, that today and tomorrow, Christ is and will be our Passover, our cleansing, our provision, our life. Your power today, to live in purity, and sanity and hope, is not found within you, but in the riches of Christ. No wonder Paul prays for the Ephesian Christians to "know . . . what are the riches of his glorious inheritance in the saints" (Eph. 1:18).