Now as they were eating, Jesus took bread, and after blessing it broke it and gave it to the disciples, and said, "Take eat; this is my body." And he took a cup, and when he had given thanks he gave it to them, saying, "Drink of it, all of you, for this is my blood of the covenant, which is poured out for many for the forgiveness of sins" (Matt. 26:26-28).
During His last supper with His disciples, Jesus "took a cup" and said that the wine in that cup was symbolic of His blood. He then stated that His blood would soon be "poured out for many for the forgiveness of sins."
The Lord's Supper is intended only for those who have experienced the forgiveness that comes from the blood of Jesus. How does a person receive this forgiveness? On an earlier occasion, Jesus declared, "Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day" (John 6:53-54).
Jesus was obviously not speaking literally when He talked about people drinking His blood. How are we to "drink his blood" so that we may be forgiven of our sins? Each one of us must individually "drink His blood" into our hearts by faith. (A cold glass of your favorite drink does you no good until you drink it.) "Whoever believes in the Son has eternal life; whoever does not obey the Son shall not see life, but the wrath of God remains on him" (John 3:36).
When you drink of the cup of the Lord's Supper, you are demonstrating that you personally have received by faith the forgiveness that is available through Christ's shed blood.