And when it was evening, he came with the twelve. And as they were reclining at table and eating, Jesus said, “Truly, I say to you, one of you will betray me, one who is eating with me.” They began to be sorrowful and to say to him one after another, “Is it I?” He said to them, “It is one of the twelve, one who is dipping bread into the dish with me. For the Son of Man goes as it is written of him, but woe to that man by whom the Son of Man is betrayed! It would have been better for that man if he had not been born.”

And as they were eating, he took bread, and after blessing it broke it and gave it to them, and said, “Take; this is my body.” And he took a cup, and when he had given thanks he gave it to them, and they all drank of it. And he said to them, “This is my blood of the covenant, which is poured out for many. Truly, I say to you, I will not drink again of the fruit of the vine until that day when I drink it new in the kingdom of God.”
Mark 14:17-25.

The passover was the defining ritual of the Jewish nation. They had come to Egypt as a family, and left 400 years later as a nation. God's judgment was about to fall on Egypt, and the Jews would be protected from that judgment by the blood of the lamb that was slain for passover.

What we call holy communion is a symbolic reenactment of that passover. Some Christians celebrate the entire passover as a means of more fully understanding their spiritual lineage. The Jews were to celebrate the passover annually to remember their deliverance from Egypt, but it also looked forward to the lamb that would take away their sin once and for all. But they would not understand that until Jesus had been slain and shed His blood to rescue us all from judgment. 

I grew up in a liturgical church that reenacted the last supper every week, listening to the priest give us the play by play on what it was all about. It could have been meaningful to me as a boy, but it wasn't. I went to church as a spectator. I never applied the meaning of it all to my life until I was an adult. After participating, I went out, and like Judas, went my own way.