The request is for position, for a place of honor measured against others, and this is why the answer is that they do not know what they ask. To seek greatness by comparison is still to believe in separation, in a kingdom where one mind can be raised above another. The cup and the baptism are not rewards for the special but the undoing of specialness itself, the willing release of every claim to be more than a brother.
A mind can say it is able while still misunderstanding entirely, imagining the path leads up when it leads through. What is asked of it is not to rise above others but to let the whole idea of ranking fall away.
Cup: what the mind must be willing to accept, not a prize but the emptying of every wish to be set apart.
Baptism: the immersion that dissolves specialness, washing away the belief that one mind stands higher than the rest.