During the Passover meal there are four cups of wine taken (usually watered down) . Wine is a symbol of the joy of the harvest, and since all the feasts given to the Jews by God center around their agricultural lives this would make sense as the beverage of choice.
Four expressions were used in Ex 6:6-7 describing His promised deliverance from Egypt.
1. "I will bring you out."
2. "I will rescue you from their bondage."
3. "I will redeem you."
4. "I will take you as my people."
When the first cup is poured, the Father of the family asks everyone to rise. He lifts his cup toward heaven and recites the Kiddush (prayer of sanctification).
Christ the leader of the Passover in the upper room took this cup and gave thanks. This is the first cup and is one of Thanksgiving.
The second cup of wine is now poured out and in response to the questions, asked earlier by the children, a lengthy narrative recounting the Passover begins. Here is where the symbolic elements are carefully explained in the telling of the story. Before this cup is taken the first half of the praise psalms, (the Hallel) is recited. Hallel means praise.
The third cup is called the cup of redemption or blessing. This is where the Lord's Supper was instituted by Christ. This was afer the dinner. This cup Jesus chose to be a reminder of His work on the cross. After this cup, a child is sent to the front door to hopefully welcome Elijah. The hope is that Elijah will come in and drink his cup of wine and announce the coming of the Messiah. This comes from the hope of Malachi 4:5.
The fourth cup is one of acceptance or Praise. This is the cup that Jesus said He would not drink until He drank it with the disciples in the Kingdom. He knew that the hour of his acceptance by His Jewish nation was yet future, and therefore His joy would not be full until then.
By tradition every Seder ends with the last half of the Hallel (Ps 115-118). Just before the Messiah and his disciples went out into the cold moonlit night, their destination being the Garden of Gethsemane, they sang these Psalms. How ironic that just before He was about to die on the cross He would sing Ps 118:22-26. This psalm was viewed as prophetically Messianic. Those in Jerusalem for the feast of Passover that week never saw Him as the Messiah that indeed had already come.