1 Corinthians 5:6-8
Your boasting is not good. Do you not know that a little leaven leavens the whole lump? 7 Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our Passover lamb, has been sacrificed. 8 Let us therefore celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth.

According to the law given by God to Moses, during the feast of Passover and Unleavened Bread, which followed and was closely connected to the Passover, the saints of old were to remember God’s gracious deliverance of His people out of the bonds of slavery in Egypt. They were to eat it in haste, “with a belt around the waist, sandals upon the feet, and a staff in the hand”.