Bible passage: Exodus 12:21-23
Written: As early as 1400 BC
In the Old Testament, just before the Exodus in which the Israelites left Egypt and returned to their homeland, they were instructed to use the blood of lambs and goats to protect themselves from God's wrath:
21 Then Moses summoned all the elders of Israel and said to them, "Go at once and select the animals for your families and slaughter the Passover lamb. 22 Take a bunch of hyssop, dip it into the blood in the basin and put some of the blood on the top and on both sides of the doorframe. None of you shall go out of the door of your house until morning. 23 When the Lord goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the doorframe and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down." (Exodus 12:21-23, NIV)
Exodus 12 is where the yearly commemoration of Passover began, where it traces its roots. It is commemorated within Judaism throughout the world. In ancient times, in the land of Israel, though, the holiday involved the sacrifice of lambs.
The sacrificing of the lambs in Exodus 12 protected the Israelites from God's wrath during the time of the Exodus, and the yearly commemoration of Passover reflects in part on that deliverance.
The death of Jesus in the New Testament served as the ultimate and final sacrifice needed for deliverance, for those who believe. In the New Testament, Jesus is compared to the Passover lamb:
7 Get rid of the old yeast, so that you may be a new unleavened batch—as you really are. For Christ, our Passover lamb, has been sacrificed. (1 Corinthians 5:7, NIV)
The writer of 1 Corinthians, which is an epistle in the New Testament, is believed to be Paul the Evangelist, who wrote about 20 years after the crucifixion of Jesus. His reference to "yeast" and "unleavened" are also references to the manner in which Passover is to be observed, in accordance to rules that Moses gave in Exodus 12.
It is important to note that Jesus was crucified during the time of the Passover holiday, and that might be another reason why the writer of 1 Corinthians alludes to the Passover in connection with Jesus' death.