1 Corinthians 10:21 - Coke's Commentary on the Holy Bible

Ye cannot drink the cup, &c.— There still remains one more sense of the Lord's supper, which is, that it was a foederal rite or covenant: this is grounded upon the Apostle's reasoning in this and the preceding verses: "Those who eat of the sacrifices, says he, are partakers of the altar: 1 Corinthians 10:18." Now a sacrifice at the altar, was a foederal rite or covenant; consequently the feast upon that sacrifice, became a foederal rite and covenant likewise. It is easy to shew that the demons were considered as present at the heathen sacrifices, and as partakers with the worshippers inthe common feast; and that by these means friendship, brotherhood, and familiarity, were imagined to be contracted between them, because they all ate at one table, and sat down at one board. The Lord's table, and the table of devils, therefore, being both foederal rites or covenants, the same person could not be a partaker of both; because no man can execute two foederal rites or covenants which mutually destroy each other. See Cudworth's "True notion of the Lord's supper," ch. 1 and 5 Elsner and Lowman's Heb. Ritual, p. 54.