The Mass of the Lord’s Supper, as its name indicates, commemorates Jesus’ last supper with his disciples before his arrest, trial, and death on the cross. The first reading — Exodus 12:1-8, 11-14 — gives the prescriptions for the Israelites’ first Passover, celebrated the night before their exodus from Egypt, with its sacrificial lamb and unleavened bread.
We see the lamb, whose blood protected the Israelites from the the destroying angel, as a prefiguring of Jesus. When John the Baptist saw Jesus, he called him “the Lamb of God, who takes away the sin of the world.” (John 1:29) Jesus’ offering of himself, his self-sacrifice, redeems us from our sinfulness. We will be able to leave the Egypt of slavery to sin and ultimately enter the promised land of heaven.
The unleavened bread prefigures the bread of the Lord’s Supper. In John 6, Jesus said that we must eat his body and drink his blood to have life, and he said that the bread he would give us is his flesh. The gospels suggest that the Last Supper was the Passover meal. At it, Jesus fulfills the promise of his flesh and blood by identifying the unleavened bread as his body and the cup of wine as his blood. We believe that at every Mass, the sacrifice of Calvary is made present as it was at the Last Supper. That is why the priest repeats John the Baptist’s words, “Behold the Lamb of God … who takes away the sins of the world.”
In the responsorial psalm — Ps 116:12-13, 15-16bc, 17-18, with a refrain based on 1 Corinthians 10:16 — we anticipate the next reading and reflect on death and sacrifice.
The second reading —1 Corinthians 11:23-26 — gives us Paul’s account of Jesus’ institution of the Eucharist at the Last Supper. It was written before the gospels, and witnesses to the tradition which informed them. Jesus declares that the bread he shares is his body, that is for them, and the wine is the new covenant in his blood. They are to repeat his action in remembrance of him — proclaiming his death until he returns.
The choice of John 13:1-15 for the gospel may seem surprising: why not one of the synoptics, with their accounts of the institution of the Eucharist? For one thing, we already have the equivalent in the second reading. For another, we have the Feast of the Body and Blood of the Lord (Corpus Christi) to underline the doctrine of the Real Presence. The account of Jesus’ washing the feet of the disciples, and commanding them to serve one another, following his example, shows us what the effect of our participation at Mass must be. Jesus didn’t give us his body and blood, sacrificed on Calvary, for their own sake. They are to gives us a life conformed to his life, a life of love for one another and of the service which naturally flows from that love. In the Latin the Church used for centuries, the word for “commandment” that Jesus uses is “mandatum,” which, in an anglicized form, “maundy” gives the title under which this day is often designated: Maundy Thursday.
Christians’ participation in the Body and Blood of the Lord must lead to loving service. I think Pope Francis is re-emphasing this point for us.