Charles Ellicott Commentary 1 Corinthians 5:8

"wherefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth." — 1 Corinthians 5:8 (ASV)

Old leaven—that is, in their old state generally; and then the Apostle proceeds to specify. Sincerity and truth are to take the place of malice and wickedness in the continuous life of the Christian. St. Chrysostom well remarks: “He said ‘Let us keep the feast’ as pointing out that the whole of time is a festival to Christians, because of the excellence of the good things which have been given.”