The cup of {n} blessing which we bless, is it not the {o} communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ?

(n) Of thanksgiving: whereupon, that holy banquet was called eucharist, which is Greek for thanksgiving.

(o) A most effectual pledge and note of your joining together with Christ, and ingrafting to him.

People's New Testament

10:16 The cup of blessing which we bless. A name applied to the cup used in the Lord's Supper. Paul shows from the nature of the Lord's Supper, and of the Jewish sacrificial feasts, that to eat in an idol feast is an idol communion.

Is it not the communion of the blood of Christ? Is not the cup the symbol of joint participation or fellowship of the blood of Christ.

Is it not the communion of the body of Christ? Is not the bread the symbol of joint participation of Christ's body?

Wesley's Notes

10:16 The cup which we bless - By setting it apart to a sacred use, and solemnly invoking the blessing of God upon it. Is it not the communion of the blood of Christ - The means of our partaking of those invaluable benefits, which are the purchase of the blood of Christ. The communion of the body of Christ - The means of our partaking of those benefits which were purchased by the body of Christ - offered for us.

Jamieson-Fausset-Brown Bible Commentary

16. The cup of blessing-answering to the Jewish "cup of blessing," over which thanks were offered in the Passover. It was in doing so that Christ instituted this part of the Lord's Supper (Mt 26:27; Lu 22:17, 20).

we bless-"we," not merely ministers, but also the congregation. The minister "blesses" (that is, consecrates with blessing) the cup, not by any priestly transmitted authority of his own, but as representative of the congregation, who virtually through him bless the cup. The consecration is the corporate act of the whole Church. The act of joint blessing by him and them (not "the cup" itself, which, as also "the bread," in the Greek is in the accusative), and the consequent drinking of it together, constitute the communion, that is, the joint participation "of the blood of Christ." Compare 1Co 10:18, "They who eat . are partakers" (joint communicants). "Is" in both cases in this verse is literal, not represents. He who with faith partakes of the cup and the bread, partakes really but spiritually of the blood and body of Christ (Eph 5:30, 32), and of the benefits of His sacrifice on the cross (compare 1Co 10:18). In contrast to this is to have "fellowship with devils" (1Co 10:20). Alford explains, "The cup . is the [joint] participation (that is, that whereby the act of participation takes place) of the blood," &c. It is the seal of our living union with, and a means of our partaking of, Christ as our Saviour (Joh 6:53-57). It is not said, "The cup . is the blood," or "the bread . is the body," but "is the communion [joint-participation] of the blood . body." If the bread be changed into the literal body of Christ, where is the sign of the sacrament? Romanists eat Christ "in remembrance of Himself." To drink literal blood would have been an abomination to Jews, which the first Christians were (Le 17:11, 12). Breaking the bread was part of the act of consecrating it, for thus was represented the crucifixion of Christ's body (1Co 11:24). The distinct specification of the bread and the wine disproves the Romish doctrine of concomitancy, and exclusion of the laity from the cup.

Matthew Henry's Concise Commentary

10:15-22 Did not the joining in the Lord's supper show a profession of faith in Christ crucified, and of adoring gratitude to him for his salvation ? Christians, by this ordinance, and the faith therein professed, were united as the grains of wheat in one loaf of bread, or as the members in the human body, seeing they were all united to Christ, and had fellowship with him and one another. This is confirmed from the Jewish worship and customs in sacrifice. The apostle applies this to feasting with idolaters. Eating food as part of a heathen sacrifice, was worshipping the idol to whom it was made, and having fellowship or communion with it; just as he who eats the Lord's supper, is accounted to partake in the Christian sacrifice, or as they who ate the Jewish sacrifices partook of what was offered on their altar. It was denying Christianity; for communion with Christ, and communion with devils, could never be had at once. If Christians venture into places, and join in sacrifices to the lust of the flesh, the lust of the eye, and the pride of life, they will provoke God.