The Last Supper
While they were eating, Jesus took a loaf of bread, and after blessing it he broke it,
gave it to the disciples, and said, “Take, eat; this is my body.” Then he took a cup,
and after giving thanks he gave it to them, saying, “Drink from it, all of you; for
this is my blood of the covenant, which is poured out for many for the forgiveness of sins.
I tell you, I will never again drink of this fruit of the vine until that day when I drink it
new with you in my Father’s kingdom.
Matthew 26, 26-29
The cup of blessing that we bless, is it not a sharing in the blood of Christ?
The bread that we break, is it not a sharing in the body of Christ?
1 Corinthians 10, 16
The event of Christ offering himself as the paschal lamb in the Last Supper is what the celebration of the Eucharist became for the New Covenant believers. That night of the Jewish Passover, Jesus transformed the traditional sacrificial meal of the Passover lamb. For us to see how this happened, we must examine the course of our Lord’s supper in the traditional manner. Jesus is celebrating or presides over the Passover Seder meal with his apostles which requires them to drink four cups of wine. Matthew, however, begins his narrative at the serving of the third cup (Berekah) or the “Cup of Salvation” since Our Lord is looking towards his own immolation as the Passover lamb (Mt 26:29; Mk 14:25).  Paul uses the “Cup of Blessing” (Berekah) to refer to the Eucharist, connecting the Seder meal to the Eucharistic sacrifice (1 Cor 10:16). The third cup actually makes present the Paschal sacrifice of Christ, the Lamb who was slain for our sins (Isa 53:7; Jn 1:29).
Yet Jesus omits the serving of the fourth cup (Hallel) or “Cup of Consummation.” This is a significant omission that joins the Eucharistic sacrifice being offered in the Seder meal to Christ’s sacrifice on the cross. In other words, they comprise one single sacrifice. The Last Supper, therefore, is a pre-presentation of our Lord’s sacrifice on the cross which is made present in the Seder meal. This one and the same sacrifice isn’t completed until Jesus partakes of the fourth cup of wine just before he dies on the cross after saying, “It is consummated” (Jn 19:29, 30; cf. Mt 27:48; Mk 15:36). 
Jesus was given sour wine on a “hyssop” branch that was used to sprinkle the lamb’s blood on the doorposts on the night of the first Passover (Ex 12:22) and by the priests in the sacrificial offerings of the Old Covenant.  This joins Christ’s sacrifice of himself to the lambs that were slaughtered and consumed by the Jews in the Seder meal which was ceremonially completed by drinking the wine in the Cup of Consummation. Thus, Christ’s sacrifice began in the upper room and was completed on Mount Golgotha.
The Holy Sacrifice of the Mass in the Catholic Church is a re-presentation of this one single sacrifice. It is the Lord’s Supper or Seder meal of the New Covenant that makes Christ’s sacrifice on the cross perpetually present as a visible sign of the marriage feast in heaven (Rev 19:9). St. Paul tells us that we need to celebrate the Eucharistic feast: “Therefore, let us celebrate the festival, not with the old yeast, the yeast of malice and evil, but with the unleavened bread of sincerity and truth” (1 Cor 5:8). In other words, we must worthily eat the flesh of the Lamb of God and drink His blood in the Blessed Sacrament to be in holy communion with God and reap the fruits of Our Lord’s sacrifice (1 Cor 11:17-22).
Hence, the Lord’s Supper isn’t just a symbolic memorial meal, as most Protestants contend, but a marriage feast that marks God’s establishment of the New Covenant in which the Eucharist makes Christ’s one eternal sacrifice present. Scripture confirms this truth in the words of consecration – “Do this in remembrance of me” – used by Jesus in the Last Supper: touto poieite tan eman anamnasin (Lk 22:19; cf. 1 Cor 11:24-25). What our Lord literally says is, “Offer this as a memorial sacrifice.” The Greek verb poiein (ποιεῖν) or “do” is used in the context of offering a sacrifice where, for instance, in the Septuagint, God uses the same word poieseis (ποιέω) regarding the sacrifice of the lambs on the altar (Ex 29:38-39). The noun anamnesis (ἀνάμνησις) or “remembrance” also refers to a sacrifice that is really or actually made present in real-time by the power of God in the Holy Spirit, as it reminds us of the actual event (Heb 10:3; Num 10:10). 
So, the Holy Sacrifice of the Mass isn’t merely a memorial of a past event but a past event actually made present in time. Christ’s Eucharistic sacrifice is the memorial or reminder of what our Lord has accomplished for us, and continues to accomplish by his single sacrifice, not what he had accomplished and is finished in time. Only the crucifixion itself remains a past historical event. Christ’s single sacrifice of himself on the cross is ever-present in the Sacrament of the Holy Eucharist.
We read in Leviticus 24:7: ‘By each stack put some pure incense as a memorial portion to represent the bread and to be a food offering presented to the LORD.’ The word “memorial” in Hebrew in the sacrificial sense is the feminine noun azkarah ( אַזְכָּרָה )which means “to actually make present.” There are many instances in the Old Testament where azkarah refers to sacrifices that are currently being offered and so are present in time (Lev 2:2,9, 6:5; 16; 5-12; Num 5:26; 10:10).  These are one and the same sacrifices that are memorially being offered in time. Jesus’ command for us to offer the bread and wine (transubstantiated into his body and blood) as a memorial offering shows that the sacrificial offering of his body and blood is made present in time over and over again while serving as a reminder of what he has accomplished for us through his one, single sacrifice of himself. Thus, the Holy sacrifice of the Mass is sacramentally a re-presentation of Christ’s sacrifice on the cross that began at the Last Supper and historically occurred on Calvary.
Sadly, Protestants argue in disbelief that Jesus is speaking metaphorically about eating his flesh and that the bread only symbolizes his body. But the Greek verbs used in John 6 (The Bread of Life Discourse) render their interpretation implausible. Throughout John 6:23-53, the Greek text uses the verb phago (φάγω) nine times. This verb means to literally “eat” or physically “consume.” Jesus repeated himself this often because of the Jews’ disbelief. He was, in a sense, challenging their faith in him while driving an important point home. In fact, many of his disciples deserted him since they knew he was speaking literally and feared he was mad. For this reason, Jesus uses an even more literal verb that describes the process of consuming food (Jn 6: 54, 55, 56, 57). This is the verb trogo (τρώγω) which means to “gnaw” “chew” or “crunch.” Though phago may be used in a metaphorical sense, trogo is never applied symbolically. 
Anyway, for further clarification, Jesus says, “For my flesh is food indeed, and my blood is drink indeed” (Jn 6:55). Jesus is responding to those who refused to believe in what he was saying. Also, when Jesus institutes the sacrament of the Eucharist at the Last Supper, he says, “This is my body and blood” (Mt 26:26; Mk 14:22; Lk 22:19-20). The Greek phrase is “Touto estin to soma mou.” So, what our Lord means to say is “This is really or actually my body and blood.” St. Paul uses the same phraseology in his First Letter to the Corinthians 11:24. Paul does reaffirm that “the cup of blessing” and “the bread of which [the Corinthians] partake” is “actual” participation in Christ’s body and blood” (1 Cor 10:16). The Greek noun koinonia (κοινωνία) denotes a “participation” that isn’t merely symbolic. 
Moreover, the Greek text in John’s Gospel uses sarx (σάρξ) which literally means “flesh.” The phrases “real food” and “real drink” contain the adjective alethes (ἀληθής) which means “really” or “truly” (Jn 6:55). This adjective is used on occasion when there is doubt concerning the reality of something, in this case, which is Jesus’ flesh really being food to eat and his blood really being something to drink for everlasting life.  Jesus is assuring his doubters that what he is literally saying is, in fact, true. The Apostles refused to desert Jesus after listening to their Master’s discourse and attended the Seder meal with him, on which occasion, they (except Judas) consumed the flesh of the sacrificed Lamb of God and drank his blood just as the Jewish people ate the flesh of the sacrificed lamb and were sprinkled with its blood for the forgiveness of sin (Ex 12:5-8; 24:8).
Early Sacred Tradition
“For not as common bread and common drink do we receive these; but in like
manner as Jesus Christ our Saviour, having been made flesh and blood for our
salvation, so likewise have we been taught that the food which is blessed by the
prayer of His word, and from which our blood and flesh by transmutation are
nourished, is the flesh and blood of that Jesus who was made flesh.”
Justin Martyr, First Apology, 66
(A.D. 155 )
“He acknowledged the cup (which is a part of the creation) as his own blood,
from which he bedews our blood; and the bread (also a part of creation) he
affirmed to be his own body, from which he gives increase to our bodies.”
Irenaeus, Against Heresies, V:2,2
(c. A.D. 190)
“It is good and beneficial to communicate every day, and to partake of the holy
body and blood of Christ. For He distinctly says, ‘He that eateth my flesh and
drinketh my blood hath eternal life.’ And who doubts that to share frequently in
life, is the same thing as to have manifold life. I, indeed, communicate four times a
week, on the Lord’s day, on Wednesday, on Friday, and on the Sabbath, and on the
other days if there is a commemoration of any Saint.”
Basil, To Patrician Caesaria, Epistle 93
“Perhaps you will say, ‘I see something else, how is it that you assert that I receive
the Body of Christ?’ And this is the point which remains for us to prove. And what
evidence shall we make use of? Let us prove that this is not what nature made, but
what the blessing consecrated, and the power of blessing is greater than that of
nature, because by blessing nature itself is changed…The Lord Jesus Himself
proclaims: ‘This is My Body.’ Before the blessing of the heavenly words another
nature is spoken of, after the consecration the Body is signified. He Himself speaks
of His Blood. Before the consecration it has another name, after it is called Blood.
And you say, Amen, that is, It is true. Let the heart within confess what the mouth
utters, let the soul feel what the voice speaks.
Ambrose, On the Mysteries, 9:50
“I am the bread of life; whoever comes to me shall not hunger,
and whoever believes in me shall never thirst.”
John 6, 35
Notes & Sources [1-3] Brant Pitre, Jesus and the Jewish Roots of the Eucharist (New York: Doubleday, 2011) [4-8] John Salza, The Biblical Basis for the Eucharist (Huntington, Ill: Our Sunday Visitor, 2008)