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]])
# the cup of the Lord
This refers to the cup of wine that people drink from when celebrating the Lord's supper.
Here "fellowship at the table" refers to fellowship among people eating a meal together. The "table of the Lord" refers to a meal that people eat to honor the Lord. Alternate translation: "It is impossible for you to be truly one with those who eat to honor the Lord and also with those who eat to honor demons"