en_tn/1co/11/25.md

the cup

It is best to translate this literally. The Corinthians knew which cup he took, so it is not simply "a cup" or "some cup" or "any cup." Possible meanings are that it was 1) the cup of wine that one would expect him to use or 2) the third or fourth of the four cups of wine that the Jews drank at the Passover meal.

Do this as often as you drink it

"Drink from this cup, and as often as you drink from it"