14 And when the hour came, he reclined at table, and the apostles with him. 15 And he said to them, “I have earnestly desired to eat this Passover with you before I suffer. 16 For I tell you I will not eat it until it is fulfilled in the kingdom of God.” 17 And he took a cup, and when he had given thanks he said, “Take this, and divide it among yourselves. 18 For I tell you that from now on I will not drink of the fruit of the vine until the kingdom of God comes.” 19 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.” 20 And likewise the cup after they had eaten, saying, “This cup that is poured out for you is the new covenant in my blood. 21 But behold, the hand of him who betrays me is with me on the table. 22 For the Son of Man goes as it has been determined, but woe to that man by whom he is betrayed!” 23 And they began to question one another, which of them it could be who was going to do this. (Luke 22:14-23)
So Jesus institutes what will come to replace the Passover. He is the Passover lamb that will be given, that will fulfill the Passover in the kingdom of God, and so he gives his body and his blood here, as a fulfillment of the Passover, and as the New Testament that will replace the old one. Some maintain that since Jesus hadn’t died yet, hadn’t yet been sacrificed he could not be giving his true body and blood yet. But that seems to forget that Jesus is God, and therefore his death and resurrection were events that had in effect, from the point of view of eternity, already happened. And then it also seems to miss the point, which seems to be the hardest one for the reformed to grasp, that he is God and can do what he wants when he wants.