14 When the hour came, Jesus and his apostles reclined at the table.15 And he said to them, "I have eagerly desired to eat this Passover with you before I suffer.16 For I tell you, I will not eat it again until it finds fulfillment in the kingdom of God."

17 After taking the cup, he gave thanks and said, "Take this and divide it among you.18 For I tell you I will not drink again from the fruit of the vine until the kingdom of God comes."

19 And he 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."

20 In the same way, after the supper he took the cup, saying, "This cup is the new covenant in my blood, which is poured out for you.

The old covenant was the sacred agreement between God and Abraham and the Jewish people which included worshiping only God and later following the commandments given by Moses.  The old covenant required sacrifices of animals and property to pay or atone for sins and thereby become righteous or right with God.  Jesus changed everything by becoming the sacrificial lamb.  He bled and his body was broken for our sins.  Holy Communion is a remembrance of this new covenant.  Now, becoming right with God requires us to accept the gift of Jesus' sacrifice by asking His forgiveness and then allowing Him to literally live in us and live through us.  He never takes away our ability to act contrary to His Spirit within us, that's why we still sin, but if you let Him, He will mold you into the man or woman He always intended you to be.