"And as they were eating, Jesus took bread, and blessed it, and brake it, and gave it to the disciples, and said, Take, eat; this is my body. And he took the cup, and gave thanks, and gave it to them, saying, Drink ye all of it; For this is my blood of the new testament, which is shed for many for the remission of sins. But I say unto you, I will not drink henceforth of this fruit of the vine, until that day when I drink it new with you in my Father's kingdom."
That is not to say that details of sacramental theology do not matter, nor that we can deny, or should want to deny, that the Universal Church has always treated the Sacrament as having a supernatural and real connection to the Living Christ by which he gives himself to the Church as the food and drink of eternal life, and that this has given the Church every reason to speak of that grace in terms of his Presence among us, and to teach it as an objective fact, though shrouded in mystery. The consensus of the Universal Church has been to read the Scriptures in such a way as to find the presence of the risen Christ in the actual elements themselves. But, in the last several centuries our sacramental theology has become seriously unbalanced in the sense of "this ought ye to have done without leaving the other undone." But one question remains: As glad as I am that we believe in the objective and Real presence of Christ, I must ask about the covenantal meaning of the Lord's Supper, Why is this missing from most of our talk about the sacrament?
Any reading of Genesis chapter fifteen in light of St. Paul's teaching about the faith of our father Abraham (yes, Christians everywhere, our father, if we believe), especially in his Epistle to the Church in Rome, and in light of what the Epistle to the Hebrews says so clearly about the shedding of blood as it relates to any covenant, shows that God took upon himself the penalty of human sin. He passed between the pieces of the sacrificed animals as Abraham had laid them out, meaning that God chose to accept the penalty if the covenant were to be broken, even though his covenant with all mankind had been broken already. The full weight of this cannot be appreciated unless we consider the words of Jesus as he held that cup in his hands: "For this is my blood of the new testament, which is shed for many for the remission of sins."
When the New Testament was written, the Greek word that most closely held the same meaning as the word b'rit (בְּרִית) which we translate as covenant, was the word diathēkē (διαθήκη) which we translate as testament. Modern people think of a covenant as merely an agreement or contract; but, like a Last Will and Testament, it requires death.
"And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance. For where a testament is, there must also of necessity be the death of the testator. For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth. Whereupon neither the first testament was dedicated without blood. For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and of goats, with water, and scarlet wool, and hyssop, and sprinkled both the book, and all the people, Saying, This is the blood of the testament which God hath enjoined unto you. Moreover he sprinkled with blood both the tabernacle, and all the vessels of the ministry. And almost all things are by the law purged with blood; and without shedding of blood is no remission (Hebrews 9:15-22)."
What we find is that they chose the word we use for testament, because they saw that it had this connection with the meaning of covenant: It required death. We see in the opening quotation from Jeremiah that the people of Israel broke the covenant, and we must then think in terms of that fifteenth chapter of Genesis and the presence of God walking between the divided body parts of the dead animals. When the Lord said, "this cup is the new covenant/testament in my blood" the disciples thought of Jeremiah's words, foretelling that God would make a new covenant. That covenant has a list of blessings:
1. The law is written in our hearts
2. God himself is our God (i.e. the true God protects us and provides our every need)
3. We know God
4. Our sins are forgiven and forgotten.
How is this possible? Only through the sacrifice of Christ, and the shedding of his blood. We broke the covenant God made with all mankind many times over. He made it with all people in creation. He made it with Abraham whose faith was credited to him for righteousness. He made it with his chosen and elect people, among whom are counted all Christians as those grafted into the people of Israel, children of Abraham by faith. On that night he made it with us anew, and to establish it he bore the full weight of death, that the New Covenant is his Testament. Our inheritance includes those benefits listed above, as Jeremiah foretold. It includes, as a necessary part of knowing God, eternal life (John 17:3), for God is eternal.
This is why when we "do this" in remembrance of Him, it is the sacrifice re-presented, in that we "show forth the Lord's death," each time we "do this," and will do so "till he come." This is not the double plural "sacrifices of masses." It is the Eucharistic sacrifice. It is the covenant meal that includes the sacrificial thanksgiving or Eucharist (literally good grace, or good thanksgiving). This is why our Canon of Consecration opens: "All glory be to thee, Almighty God, our heavenly Father, for that thou, of thy tender mercy, didst give thine only Son Jesus Christ to suffer death upon the Cross for our redemption; who made there (by his one oblation of himself once offered) a full, perfect, and sufficient sacrifice, oblation, and satisfaction, for the sins of the whole world." This sets the stage for all that follows.
That communion, or fellowship (koinōnia, κοινωνία) with the Body and Blood of Christ is communion with one another in the Church, which is also called by the same name, "the Body of Christ" (I Corinthians 12). The unworthy or wicked person who presumes to eat and drink is guilty of the body and blood of the Lord, in terms of the whole ancient understanding of what a covenant means. In the context of St. Paul's warning, in that eleventh chapter, the unworthy or wicked person is known by how he mistreats his brothers and sisters, those also in the communion of Christ's Body, those also in the covenant.