Sacrifices were in old times accompanied by feasts in which the reconciled God and His worshippers ate together. In the feast of Passover the lamb which had been used as a sacrifice was consumed as food to strengthen the Israelites for their exodus. This idea Paul here adapts to his present purpose. "Christ our passover is sacrificed for us," he says; "let us therefore keep the feast." The whole life of the Christian is a festal celebration; his strength is maintained by that which has given him peace with God. By Christ's death God reconciles us to Himself; out of Christ we continually receive what fits us to serve God as His free people. Every Christian should aim at making his life a celebration of the true deliverance Christ has accomplished for us. We should see that our life is a true exodus, and being so it will bear marks of triumph and of freedom. To feed upon Christ, joyfully to assimilate all that is in Him to our own character, it is this which makes life festal, which turns faintness into abounding strength, and brings zest and appetite into monotonous labour.
But Paul's purpose in introducing the idea of the Passover is rather to enforce his injunction to the Corinthians to purge their communion of all defilement. "Let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness!" Leaven was judged unclean, because fermentation is one form of corruption. This impurity was not to be touched by the holy people during their festival week. This was secured at the first keeping of the Passover by the suddenness of the exodus when the people fled with their kneading boards on their shoulders and had no time to take leaven, and had therefore no choice but to keep God's command and eat unleavened bread. And so scrupulously did the people at all times observe this that before the day of the feast they used to sweep their houses and search the dark corners with candles, lest a morsel of leaven should be found among them. Thus would Paul have all Christians be separate from the rotting, fermenting results of the old life. So suddenly would he have us issue from it and so clean would He have us leave it all behind us. A _little_ leaven leaveneth the whole lump; therefore must we be careful, if we would keep this precept and be clean, to search into even unlikely corners in our hearts and lives, and as with the candle of the Lord make diligent search for the tainting remnant.
It is the purpose to keep the feast faithfully, and live as those who are delivered from bondage, which reveals in our consciousness how much we have to put away, and how much of the old life is following on into the new. Habits, feelings, likings and dislikings, all go with us. The unleavened bread of holiness and of a life bound to and ruled by the earnest and godly life of Christ, seems flat and insipid, and we crave something more stimulating to the appetite. The old intolerance of regular, intelligent, continuous prayer, the old willingness to find a rest in this world, must be purged out as leaven which will alter the whole character of our life. Are our holy days holidays, or do we endure holiness of thought and feeling mainly on the consideration that holiness is but for a season? Patiently and believingly resist the stirrings of the old nature. Measure all that rises in you and all that quickens your blood and stirs your appetite by the death and spirit of Christ. Sever yourself determinedly from all that alienates you from Him. The old life and the new should not run parallel with one another so that you can pass from the one to the other. They are not side by side, but end to end; the one all preceding the other, the one ceasing and terminating where the other begins.