And when the hour came, he reclined at table, and the apostles with him. And he said to them, “I have earnestly desired to eat this Passover with you before I suffer. For I tell you I will not eat it until it is fulfilled in the kingdom of God.” And he took a cup, and when he had given thanks he said, “Take this, and divide it among yourselves. For I tell you that from now on I will not drink of the fruit of the vine until the kingdom of God comes.” And he took bread, and when he had given thanks, he broke it and gave it to them, saying, “This is my body, which is given for you. Do this in remembrance of me.” And likewise the cup after they had eaten, saying, “This cup that is poured out for you is the new covenant in my blood. But behold, the hand of him who betrays me is with me on the table. For the Son of Man goes as it has been determined, but woe to that man by whom he is betrayed!” And they began to question one another, which of them it could be who was going to do this. Luke 22:14-23.
What is almost universally described as The Last Supper is also the description of the new covenant. The old covenant provided forgiveness of sins through the death of an innocent animal, which was only a symbol of the innocent Son of God. So Jesus is not co-opting the passover, but revealing what it really meant all along.
The New Testament was written to explain the heavenly significance of the earthly requirements of God’s law. “Thus it was necessary for the copies of the heavenly things to be purified with these rites, but the heavenly things themselves with better sacrifices than these. For Christ has entered, not into holy places made with hands, which are copies of the true things, but into heaven itself, now to appear in the presence of God on our behalf. Nor was it to offer himself repeatedly, as the high priest enters the holy places every year with blood not his own, for then he would have had to suffer repeatedly since the foundation of the world. But as it is, he has appeared once for all at the end of the ages to put away sin by the sacrifice of himself. And just as it is appointed for man to die once, and after that comes judgment, so Christ, having been offered once to bear the sins of many, will appear a second time, not to deal with sin but to save those who are eagerly waiting for him.” (Hebrews 9:23-28).
Knowing these things help us to understand that God has not changed since Jesus’s death and resurrection. He has only been more perfectly revealed.