14 Therefore, my beloved, shun the worship of idols.
15 I speak as to sensible men; judge for yourselves what I say.
16 The cup of blessing which we bless, is it not a participation in the blood of Christ? The bread which we break, is it not a participation in the body of Christ?
17 Because there is one bread, we who are many are one body, for we all partake of the one bread.
18 Consider the people of Israel; are not those who eat the sacrifices partners in the altar?
19 What do I imply then? That food offered to idols is anything, or that an idol is anything?
20 No, I imply that what pagans sacrifice they offer to demons and not to God. I do not want you to be partners with demons.
21 You cannot drink the cup of the Lord and the cup of demons. You cannot partake of the table of the Lord and the table of demons.
Note that some translations have "communion" in place of "participation" in verse 16. Notice also (v. 17) that the Eucharist is the bond that joins Christians as well as being a symbol of their unity. This agrees with the description of the first Christians in Acts 2:42, which implies that the eucharist was a cause of their unity: "And they devoted themselves to the apostles' teaching and fellowship, to the breaking of bread and the prayers."
Notice how St. Paul draws a parallel pagan sacrifices and the Eucharist; the former is offered to demons, the latter to God: "By eating the meat of animals offered to Yahweh, Jews participated in the sacrifice and worship in his honour; and by receiving the body and blood of the Lord, Christians unite themselves to Christ; similarly, those who take part in idolatrous banquets are associating themselves not with false gods--which have no existence-- but with demons." (Navarre Bible, commentary on vv. 14-22) Thus, the Eucharist is a sacrifice to God.This teaching of St. Paul also brings out the full meaning of chapter seven of the Letter to the Hebrews, in which Christ is called ``a priest forever in the line of Melchizedek'' (cf. Psalm 110:4). Melchizedek offered bread and wine as his sacrifice to God (Genesis 14:17-20), a sacrifice which foreshadowed Jesus' own sacrifice. For Christians, the Holy Eucharist is the unbloody renewal of the sacrifice of Calvary. It is not a new sacrifice, but a continuation of our Lord's self-immolation, which transcends all time and place. In communion, a Christian receives our Lord and also offers himself to the Lord: it is an exchange of persons. To the early Christians this exchange must have been painfully obvious, since their participation in the Eucharistic feast implied their willingness to confess Christ even to death.