On the first day of the Feast of Unleavened Bread, the disciples came to Jesus and asked, “Where do you want us to make preparations for you to eat the Passover?” He replied, “Go into the city to a certain man and tell him, ‘The Teacher says: My appointed time is near. I am going to celebrate the Passover with my disciples at your house.’” So the disciples did as Jesus had directed them and prepared the Passover. (Matthew 26:17-19)
The preparations about which the disciples were asking were extensive.
Toward mid afternoon of Thursday, the lambs (one per "household") would be brought to the temple court where the priests sacrificed them. The priests took the blood and passed it in basins along a line till it was poured out at the foot of the altar. They also burned the lambs' fat on the altar of burnt offerings. The singing of the Hallel (Psalms 113-18) accompanied these steps.
As opposed to our 24-hour clock, In the Hebrew culture, the next day did not begin at midnight, but after sunset. So, once the sun went down, it became “Friday.” The "household" would gather in a home to eat the Passover lamb.
Searching for the Leaven
According to Leviticus 23:6 and Numbers 28:17, Jews were forbidden to use yeast in their bread for seven days during and after Passover. Exodus 12:18 says that yeast should be removed from the house on Thursday. So, at noon of Thursday, all the leaven (the yeast) in the house was taken out.
This was to remind the Israelites of their hurried departure from Egypt, when without waiting to bake leavened bread they carried dough and kneading-troughs with them, baking as they wandered.
The prohibition on leaven was also used as a teaching device: fermentation implied disintegration and corruption, and to the Hebrew anything in a decayed state suggested uncleanness. Rabbinical writers often used leaven as a symbol of evil and of man’s hereditary corruption. Just as the leaven works its way through a whole loaf of bread, so our sin can and very often does work its way through the entire family of God.
The First Cup
To start out the feast, the head of the household would pray, giving thanks for the feast day (the Passover Kiddush) and for the wine, praying over the first of four cups to be drunk throughout the meal. A preliminary course of greens and bitter herbs was followed by the Passover haggadah--in which a boy would ask the meaning of all this, and the head of the household would explain how the symbols pertain to the Exodus.
The Passover, he would explain, is the celebration of God “passing over” the Israelites when they were in Egypt. He would recount the story from Exodus 11 and 12—of how Pharaoh refused to let God’s people go, and how, as a final blow against the evil of the Egyptians, God would kill every firstborn in Egypt, but would spare the Israelites of the same fate:
“On that same night I will pass through Egypt and strike down every firstborn—both men and animals—and I will bring judgment on all the gods of Egypt. I am the LORD. The blood will be a sign for you on the houses where you are; and when I see the blood, I will pass over you. No destructive plague will touch you when I strike Egypt.“This is a day you are to commemorate; for the generations to come you shall celebrate it as a festival to the LORD—a lasting ordinance. (Exodus 12:12-14)
After explaining this, they would sing the first part of the Hallel (Ps 113 or Pss 113-14).
The Second Cup
Then a second cup of wine introduced the main course—the Passover Lamb, which had been roasted with bitter herbs.
It was at this juncture that Matthew 26:20-25 occurred:
When evening came, Jesus was reclining at the table with the Twelve. And while they were eating, he said, “I tell you the truth, one of you will betray me.” They were very sad and began to say to him one after the other, “Surely not I, Lord?” Jesus replied, “The one who has dipped his hand into the bowl with me will betray me. The Son of Man will go just as it is written about him. But woe to that man who betrays the Son of Man! It would be better for him if he had not been born.” Then Judas, the one who would betray him, said, “Surely not I, Rabbi?” Jesus answered, “Yes, it is you.”
The NIV is misleading: it gives the impression that a particular "one" is in view, when in fact most if not all those present would have dipped into the same bowl as Jesus, given the eating styles of the day.
Jesus' point is that the betrayer is a friend, someone close, someone sharing the common dish, thus heightening the enormity of the betrayal. Judas does indeed betray Jesus--in spite of what the "Gospel of Judas" contends (for information that clearly refutes the recent media fuss of the gnostic gospel of Judas, see Mark Goodacre's "megapost" that links to many resources on the subject)
Next: The Third Cup--the announcement that Jesus is offering a NEW EXODUS AND RESCUE to his followers.