What does Mark 14:25 mean?
To understand this better, we have to look at a few verses before it
“21. Yes, the Son of man is going to his fate, as the scriptures say he will, but alas for that man by whom the Son of man is betrayed! Better for that man if he had never been born.’ 22. And as they were eating he took bread, and when he had said the blessing he broke it and gave it to them. ‘Take it,’ he said, ‘this is my body.’ 23. Then he took a cup, and when he had given thanks he handed it to them, and all drank from it, 24. and he said to them, ‘This is my blood, the blood of the covenant, poured out for many.”
“25. In truth I tell you, I shall never drink wine any more until the day I drink the new wine in the kingdom of God.'” (New Jerusalem Bible)
Jesus was telling his disciples that his mission on earth has come to an end, “The son of man is going to his fate”. He then instituted the Holy Eucharist which we celebrate to this day in Mass. The Last Supper (and the Mass) is a foretaste of the coming feast in Heaven
“6. On this mountain, for all peoples, Yahweh Sabaoth is preparing a banquet of rich food, a banquet of fine wines, of succulent food, of well-strained wines.”
(Isiah 25;6 New Jerusalem Bible)