Drinking from the cup of the Lord is a symbol of being united to the Lord, and drinking from the cup of demons is a symbol of being united to demons. It is impossible to be united to both the Lord and demons. Alternate translation: "You cannot be united to the Lord by drinking from his cup and also be united to demons by drinking from their cup (See: [[rc://en/ta/man/translate/translate-symaction]])
Here "cup" is a metonym for the wine in the cup. Alternate translation: "You cannot drink from the cup" or "You cannot drink the wine from the cup" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Here "have fellowship at the table" refers to eating a meal together. The "table of the Lord" refers to a meal that people eat to honor the Lord. Alternate translation: "You cannot eat together at the table of the Lord and at the table of demons" or "You cannot join in eating to honor the Lord and join in eating to honor demons"