The Passover and Feast of Unleavened Bread were instituted on the evening of Israel’s deliverance from Egypt. After God had performed nine signs to convince the Pharoah to let Israel go, He announced to Moses the last plague. About midnight the LORD said He would go throughout Egypt and kill all the firstborn of man and animals.
The firstborn of the children Israel would be saved if they killed a lamb and put the blood on the doorposts and lintel of their houses. When God passed through Egypt, He passed over the firstborn on whose houses the blood was applied. They were to eat unleavened bread for they must be ready to leave in haste – no time for bread to rise! They were to remove all the leaven from their houses. This feast was to be observed when they entered the land of Canaan to remember the day they went out from Egypt (See Exodus 11-13).
In 1 Corinthians 5:6-8, Paul illustrates the removal of an immoral brother from the church citing the Feast of Unleavened Bread and the removal of leaven. By taking this action the church would be a new lump (of dough). What is fascinating is that they were already a new lump because Christ, our Passover was sacrificed for us! As a church, and as individual Christians, we must remove the old leaven of past sins (Paul cites malice and wickedness), and those who continue in them. We must as the church and believers keep the feast, that is, worship and serve God with the unleavened bread of sincerity and truth.