Was it a Seder meal Jesus kept on the night He was betrayed? Simple answer. No.
This is what He said to His disciples as they gathered for the Passover meal.
“Then He said to them, “With fervent desire I have desired to eat this Passover with you before I suffer;”
Luke 22: 14
So, there’s the first reason. Jesus said it was a Passover meal, and Jesus never lied.
There was no need for a Seder meal
The Seder meal replaced the Passover when it was no longer possible to sacrifice the Passover lambs. (Destruction of the Temple in Jerusalem 70AD)
When Jesus was about to be crucified the Passover was still being kept.
Some were keeping the 14th Passover and keeping it as commanded, others would keep it during the day part of the Passover, on the 15th and be part of the Temple Passover. (Remember the Hebrew day began at sunset on the day before.)
So, again, why do I say there was no need for a Seder meal?
While it was still possible for the Passover to be sacrificed, the Seder substitute was not necessary.
To be honest, it is hard to find a reference that does not amalgamate the two. But the Seder meal began after there was no Passover Lamb sacrifice. That’s why only a lamb shank is on the Seder plate.
Jesus kept a Passover meal
That’s why He said it.
But it was in two parts. (Judas left to betray Christ after the Passover meal, and before the New Testament Passover.)
The Passover ended the First (Old Covenant). Remember my post about the significance of the Covenants? https://www.susanprestonauthor.com/old-covenant-new-covenant/
A covenant could only be broken by the death of the person making the covenant. God had a covenant with Israel. The only way to have a New Covenant was for Jesus, God in the flesh, to die. And that’s the second part of the covenant.
The Passover meal and Jesus Covenant death, ended the Old Covenant and enabled the New Covenant to be in effect.
The bread and wine began the New Covenant. This New Covenant Passover is kept by many Christians today.
Some thoughts to ponder upon,
More info about the Seder plate:
Seder plate image
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Seder plate arrangement