Adam Clarke on 1 Corinthians 10:21

Ye cannot drink the cup of the Lord - It is in vain that you who frequent these idol festivals profess the religion of Christ, and commemorate his death and passion in the holy eucharist; for you can not have that fellowship with Christ which this ordinance implies, while you are partakers of the table of demons. That the Gentiles, in their sacrifices, fed on the slain beasts, and ate bread and drank wine in honor of their gods, is sufficiently clear from various accounts. See my Discourse on the Holy Eucharist, where many examples are produced. The following from Virgil, Aen. viii, verse 179-273, is proof in point: -

Tum lecti juvenes certatim araeque sacerdos

Viscera tosta ferunt taurorum, onerantque canistris

Dona laboratae Cereris, Bacchumque ministrant.

Vescitur Aeneas simul et Trojana juventus

Perpetui tergo bovis et lustralibus extis. -

Quare agite, O juvenes, tantarum in munere laudum,

Cingite fronde comas, et pocula porgite dextris,

Communemque vocate Deum, et date vina volentes.

The loaves were served in canisters; the wine

In bowls; the priests renewed the rites divine:

Broiled entrails are their food, and beef's continued chine

Ye warlike youths, your heads with garlands crown,

Fill high the goblets with a sparkling flood,

And with deep draughts invoke our common god.