We need to reconsider why it was that Jesus chose Passover (a night of celebrating and remembering liberation) rather than Yom Kippur, the Day of Atonement (a day of affliction and a day when sins were atoned for). Why does he choose this night to take his stand for what his death meant? Why die at Passover instead of Yom Kippur?
Details about these feasts can be found by reading Leviticus 16 and 23. It could be that Passover was a pilgrim festival, and hence attended by more, and Yom Kippur was not. From the “triumphal entry” forward, Jesus was aware of mounting opposition to what he was doing. That he stayed the course is significant. He could have escaped from Jerusalem and returned to Galilee in the quiet of the night. Aware of the opening chasm of death before him, Jesus chose to stay and he chose to die.

Again, we ask: Why choose Passover for his death?
We answer that by answering this question: What did death at Passover do? Passover involved the death of a lamb; it involved the smearing of a lamb’s blood with the hyssop branch on the door; the blood protected from God’s judgment and liberated Israel following that protection. If this is what Passover was about, then — if we think about this historically — Jesus was “storifying” his own death: Jesus was claiming that his followers, by ingesting his body and blood, were (as it were) “smearing” blood on themselves to protect themselves from the judgment of God against the oppressive, violent, and power-mongering leaders of Israel and Rome who right now were oppressing God’s good people. We need to recall that Jesus had just announced (read Mark 13) that judgment would shortly come to Jerusalem.
If we are willing to think about what this might have meant to the first followers of Jesus, it could conclude this: the Last Supper was an act of rebellion against Rome and Israel’s unjust leaders and the claim that those who “ingest” Jesus will be protected from judgment and liberated — like escaping beyond the Red Sea — to live in the kingdom of God. By choosing Passover instead of Yom Kippur to explain his death, Jesus chooses the images of divine protection and liberation. He offers himself—in death—to absorb the judgment of God on behalf of his followers so he can save his people from their sins.
No one would argue that this is all there is to the death of Jesus — there are many other images one could explore, but one must begin right here: Jesus’ act at the Last Supper declares that his death is atoning, that his blood is like the Passover blood, that his death will save his followers from their sins, and that his death will create the new covenant community around him.