You cannot drink the cup of the Lord and the cup of demons too; you cannot partake in the table of the Lord and the table of demons too.
In this passage the apostle urges the general caution against idolatry, in the particular case of eating the heathen sacrifices as such, and out of any religious respect to the idol to whom they were sacrificed. I. He prefaces his argument with an appeal to their own reason and judgment: "I speak to wise men, judge you what I say, Co1 10:15.
Commenting on 1 Corinthians 10:15-22
Ye cannot drink the cup of the Lord, and the cup of devils,.... Not only they ought not, but they could not rightly, truly, and really drink the cup of wine in the Lord's supper, in the true faith of Christ's bloodshed, and his sacrifice offered up for them, in remembrance of his love, and to the honour of his name; and also the cup...
Verse 21. Ye 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, decent.