Verse 25 reads, "This cup is the new covenant in My blood." It employs a figure of speech in which the word "cup" is a metonymy, meaning that the cup represents what it contains: literally wine. The wine symbolized His blood, thus, "This cup is the new covenant in My blood."
A covenant is an agreement, a contract, between two parties. It is a device to bring people into a binding relationship to accomplish some undertaking. This particular covenant is unusual in that it is in His blood.
In his commentary on I Corinthians 11:23-34 (p. 104), William Barclay makes a very interesting comment on this. He changes a few words and provides proof that the change is grammatically legitimate. He paraphrases it in this manner: "This covenant cost Me My life." This agreement, the New Covenant, is made at the cost of the most precious, the most valuable and dearest Life that has ever lived on the face of the earth, that of our sinless Creator. It did not come cheaply.
Barclay's paraphrase is justifiable because the life of the flesh is in the blood (Leviticus 17:14). The giving of that specific Life by His shed blood made possible the establishment of a covenantal relationship with God. This relationship is the fruit of Christ's sinless life and subsequent death. Passover portrays what makes salvation a reality for us because justification before God is its fruit. We can consider Christ's making this relationship possible the most important accomplishment of all that He has done through His death.
Our relationship with God is our salvation. We could have no salvation unless the relationship existed because we would still be cut off from God. Once established, this relationship must be developed and to be developed, it must be continued! "If you continue, you will become free," says Jesus. This begins the process of truly coming to know God, and to know God is eternal life (John 17:3).
Within the context of I Corinthians 11, a major point deals with people not properly discerning the sacred gravity of what the symbols represent. Some in Corinth were making a mockery of the Passover. The church members gathered for a meal, and some were getting drunk, others ate in a gluttonous manner, while a few received little food because others were hogging it all. What they did edified the body not at all! They experienced very little of the right kind of spiritual fellowship.
The apostle writes his epistle to correct a corrupt situation. His point is that, in doing what they did, they were not discerning the broken body and the shed blood of Jesus Christ. If they had truly understood their significance, they would not have acted in this manner. They were not properly interpreting and applying the meaning to their own lives. In treating Christ's sacrifice in a frivolous manner, their application especially went awry. They went through the motions of taking the Passover but without appreciating the reality that the symbols represented.
The word "unworthy" in I Corinthians 11:27 means "lacking in merit or worth." The Corinthians had no appreciation of the precious value of what the symbols represented to their personal salvation. They were missing the eternal character of what they were observing, caring little about who had died and grasping almost nothing of the love that went into His act. They were truly profaning the broken body and shed blood of Jesus Christ and putting Him to an open shame.
A major point of understanding about observing Passover is that our attitude toward Christ's sacrifice affects our approach to life in general. Above all, it will affect our relationship with the Father, as well as with one another, because the strength of our obligation to submit to Jesus Christ will be diminished. We will not feel it all that important to submit in obedience.
If God wants us to understand anything by our observing the Passover, it is 1) the tremendous costs it took to free us and to maintain that freedom, and 2) how far Jesus Christ, our Example, was willing to be "pushed" without giving in to sin in even the smallest of matters. Let us take Passover soberly, with the serious significance of what it represents at the forefront of our minds.