Albert Barnes Commentary 1 Corinthians 10:21

"Ye cannot drink the cup of the Lord, and the cup of demons: ye cannot partake of the table of the Lord, and of the table of demons." — 1 Corinthians 10:21 (ASV)

You cannot drink the cup of the Lord, etc. This does not mean that they had no physical ability to do this, or that it was a natural impossibility, for they certainly had power to do it. But it must mean that they could not consistently do it. It was not fit, proper, or decent. They were solemnly bound to serve and obey Christ; they had devoted themselves to Him, and they could not, consistently with these obligations, join in the worship of demons. This is a striking instance in which the word "cannot" is used to denote not natural but moral inability.

And the cup of devils. Demons (1 Corinthians 10:20). In the feasts in honor of the gods, wine was poured out as a libation or drunk by the worshipers. (See Virgil, Aeneid 8.273). The custom of drinking toasts at feasts and celebrations arose from this practice of pouring out wine or drinking in honor of the heathen gods, and it is a practice that still partakes of the nature of heathenism.

It was one of the abominations of heathenism to suppose that their gods would be pleased with the intoxicating drink. Such a pouring out of a libation was usually accompanied with a prayer to the idol god, asking that he would accept the offering, that he would be propitious, and that he would grant the desire of the worshiper.

From that custom, the habit of expressing a sentiment or proposing a toast while drinking wine has been derived. The toast or sentiment that now usually accompanies drinking a glass in this manner, if it means anything, is also now a prayer.

But to whom is this prayer addressed? To the god of wine? To a heathen deity? Can it be supposed that it is a prayer offered to the true God—the God of purity? Has Jehovah directed that prayer should be offered to Him in such a manner? Can it be acceptable to Him? Either the sentiment is meaningless, or it is a prayer offered to a heathen god, or it is a mockery of JEHOVAH; and in either case, it is improper and wicked.

And it may be said as truly now of Christians as in the time of Paul, "You cannot consistently drink the cup of the Lord at the communion table, and the cup where a prayer is offered to a false god, or to the dead, or to the air; or when, if it means anything, it is a mockery of JEHOVAH." Now, can a Christian with any more consistency or propriety join in such celebrations, and in such meaningless or profane libations, than he could go into the temple of an idol and partake of the idolatrous celebrations there?

And of the table of devils. Demons. It is not necessary for the force of this that we should suppose that the word necessarily means evil spirits. They were not God, and to worship them was idolatry. The apostle means that Christians could not consistently join in the worship that was offered to them or in the feasts celebrated in honor of them.