Jesus was talking to people who were well-educated scholars of Torah, who had grown up with the yearly observance of Passover. Their ancestors had been told by Moses to "Remember this day, in which you came out from Egypt, out of the house of bondage; for by strength of hand the LORD brought you out from this place: there shall no leavened bread be eaten." (b) They did remember that only unleavened bread be eaten during the festival, but Jesus had often pointed out that they were experts at the small stuff of the Law but missed the main points. They had apparently forgotten that yes, they had been slaves in Egypt, and were delivered by the strength of God's hand. They didn't seem to realize that without the saving hand of God, they were still in slavery to sin.
We find all through Scripture the command to "Remember!" God repeatedly promised to remember the covenants made first with Noah, then Abraham, Isaac and Jacob, then Moses. In turn: "In days to come, when your son asks you 'What does this mean?' say to him, 'With His mighty hand the Lord brought us out of Egypt, out of the land of slavery.'" (c) "You shall remember all the way which the LORD thy God led you these forty years in the wilderness, to humble you, and to know what was in your heart, whether you would keep His commandments, or not." (d) We find the call to remembrance throughout the Psalms and the prophets.
Jesus called his followers to remember something even more important than what God had done in the past--what He was preparing to do: sacrifice His own body and blood to so that our sins and failures could be forgotten. The writer of Hebrews remembers the promise to Jeremiah: "This is the covenant I will make with them after that time, says the Lord. I will put my laws in their hearts, and wil I write them on their minds...Their sins and lawless acts I will remember no more." (e) And he adds "And where these have been forgiven, there is no longer any sacrifice for sin." (f)
And this is what we are to remember: "Jesus took bread, gave thanks, and broke it, and gave it to them, saying, This is my body given for you, do this in remembrance of Me. In the same way, He took the cup, saying, This cup is the new covenant in My blood, which is poured out for you." (g) We are to remember not just the bread and the cup themselves, but that we were once slaves to sin but through a new covenant have been made His redeemed sons and daughters.
(a)John 8:31-32 (b)Exodus 13:3 (c)Exodus 13:14 (d) Deuteronomy 8:2 (e)Jeremiah 31:33-34 (f)Hebrews 10:18 (g)Luke 22:19-20