"Therefore, let us keep the Festival, not with the old yeast … but with bread without yeast" (1 Cor. 5:8).
Paul tells the Corinthians that they had no reason to boast in their religious state; on the contrary, they had many reasons to be alarmed. They had allowed sin to grow among them. “A little leaven spreads through the whole lump.” The leaven is sin, and a single sin, no matter how secret, once it is indulged diffuses its corrupting influences over the whole body.
We are, then, exhorted by the apostle to purge out the old leaven, the old man, the wickedness, that we might be pure and holy. “When the paschal lamb was slain, the Hebrews were required to purge out all leaven from their houses (Ex. 12:15),” Hodge wrote. “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 doorposts 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 dies 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.
“Let us therefore keep the feast. That is, since our passover Christ is slain, let us keep the feast. This is not an exhortation to keep the Jewish passover—because the whole context is figurative, and because the death of Christ is no reason why the Corinthians should keep the Jewish passover.… A feast was a portion of time consecrated to God. To keep the feast means, ‘Let your whole lives be as a sacred festival, i.e. consecrated to God.’ ” The feast of the passover lasted seven days and was connected to the slaying of the paschal lamb. Likewise, a life of consecration to God should be connected with the death of Christ. This feast should be celebrated not with the old leaven of wickedness but with sincerity and truth, outward conformity as well as inward conformity to the character of God.
What are some practical ways you can get rid of the “old yeast”? Make a list of sins that are most hindering in your life right now. Think of anything that you are doing that in any way encourages these sins. Systematically, and prayerfully, stop doing (or thinking of) those things that lead you to sin.