The four cups of Passover are deeply symbolic. They have been around in Jewish tradition for thousands of years. Two cups are drank before dinner, and the other two after dinner.
The cups are based on the four "I Will" statements from Exodus 6:6-7. Therefore say to the children of Israel: ‘I am the Lord; I will bring you out from under the burdens of the Egyptians, I will rescue you from their bondage, and I will redeem you with an outstretched arm and with great judgments. I will take you as My people, and I will be your God. Then you shall know that I am the Lord your God who brings you out from under the burdens of the Egyptians.
The first cup is the cup of Sanctification. That word means holy, or set apart. God set apart the Israelites as His chosen people. In the Seder, the first cup is called the Kiddush, which comes from the same root word as Kadosh, meaning holy.
The second cup is the cup of Judgement. When Yeshua was praying in the garden, He asked his father to take this cup from him. But to do His father's will, He agreed to "drink of it" so that we would not have to.
The third cup is the cup of Redemption. Just as the Lord God redeemed Israel from Egypt with an outstretched arm, so too did Yeshua redeem us with His outstretched arm on the cross. During the Seder that night, Yeshua instutited the new covenant, which had been promised to Israel in Jeremiah 31:31. Luke 22:20 tells us, Likewise He also took the cup after supper, saying, "This cup is the new covenant in My blood, which is shed for you. Jesus was literally sealing the new covenant promise with this third cup of the Seder, the Cup of Redemption. He did not drink of it Himself, therefore excluding Himself from redemption so that He could become redemption for us. He gave the cup to His disciples to drink, in order to seal the deal with them.
The fourth cup, called the Cup of Praise, is reserved for the future wedding of the Lamb. This is why Yeshua promised that He would not drink of the fruit of the vine with them until the Kingdom of God is set up on Earth when He returns.
Jesus came to Earth to become our sacrificial Passover Lamb. This is the pivotal point of all history, the fulfillment of God's promise in the garden to send a redeemer who would crush satan's head.
I was an adult before I knew that the "Last Supper" was a Passover Seder.
I don't know about you, but it seems quite incongruous to me to celebrate our redemption by the Passover Lamb with an Easter Ham... just sayin'!