The Fourth Cup

This has been said elsewhere already, namely by Scott Hahn and his protege Brant Pitre, but here Dr. Fonseca summarizes the explanation so concisely:

During the Passover Meal, Jesus did not drink of the cup for the fourth time. At the third drinking of the cup, Jesus said, “This  cup is the new covenant in my blood, which will be shed for you” (Luke 22:20). Jesus did not end the meal in the Upper Room in the established tradition which was to drink from the cup for the fourth time. Drinking from the cup for the fourth time signaled the end of the Passover meal in which the sacrificed lamb was eaten. In the new Passover Feast, the meal takes place first in which Jesus offers us His body to eat, and His blood to drink. The new Passover Feast was a meal eaten in anticipation of Jesus’ sacrifice on the cross. However, during His agony, Jesus struggles to accept the drinking of the fourth cup and go to His death on the cross. But by the end of His stay in the garden, Jesus accepts to drink of His cup and go to His crucifixion and death. On the cross, just before He dies, Jesus drinks of the cup for the fourth time. The fourth cup was drunk with just a sip. The crucified Jesus takes a sip from the wine handed to Him on a sponge, and then exclaims, “It is finished.” The Passover Meal always ended when the head of the household proclaimed the words, “It is finished.” Thus the New Passover Meal was begun in the Upper Room and ended on the Cross. In doing so, Jesus created a seamless connection between meal and sacrifice, between the Upper Room and Calvary. In the Exodus Passover Meal, the meal followed the sacrifice of the lamb. In the New Passover Meal, the meal anticipated the sacrifice of Jesus, our Lamb, on the cross!

Of course the most masterful reflections on this subject come from the late great Pope Benedict:

https://www.thecatholicthing.org/2023/04/07/the-new-adam-and-the-new-woman/