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.
21. Ye cannot drink the cup of the Lord—really and spiritually; though ye may outwardly (1Ki 18:21).
cup of devils—in contrast to the cup of the Lord. At idol feasts libations were usually made from the cup to the idol first, and then the guests drank; so that in drinking they had fellowship with the idol.
the Lord's table—The Lord's Supper is a feast on a table, not a sacrifice on an altar. Our only altar is the cross, our only sacrifice that of Christ once for all. The Lord's Supper stands, however, in the same relation, analogically, to Christ's sacrifice, as the Jews' sacrificial feasts did to their sacrifices (compare Mal 1:7, "altar … table of the Lord"), and the heathen idol feasts to their idolatrous sacrifices (Isa 65:11). The heathen sacrifices were offered to idol nonentities, behind which Satan lurked. The Jews' sacrifice was but a shadow of the substance which was to come. Our one sacrifice of Christ is the only substantial reality; therefore, while the partaker of the Jew's sacrificial feast partook rather "of the altar" (1Co 10:18) than of God manifested fully, and the heathen idol-feaster had fellowship really with demons, the communicant in the Lord's Supper has in it a real communion of, or fellowship in, the body of Christ once sacrificed, and now exalted as the Head of redeemed humanity.