1 Corinthians 5:7–8 (KJV 1900)
7 For even Christ our passover is sacrificed for us: 8 Therefore 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.
Christ our Passover. Paul’s use of this phrase makes it pretty clear he is writing to a primarily Jewish congregation. Gentiles would not have participated in the Passover. Let us keep the feast makes it more evident about the nature of this congregation. Likewise, Gentiles would not have kept the feast of Passover, nor been required to do so. This is not referring to the Lord’s Supper as some have tried to make it into.
His whole point is that the church needs to end its boasting, pride, and divisiveness. Christ was sacrificed for a pure church. Clean out the things that have made their way into the church, like malice and wickedness, Then the church can keep the feast together as they gather in sincerity and truth.