They still believed that he would be an earthly monarch, notwithstanding that he had just told them of his speedy death. Ye know not what ye ask. An illustration, this of ignorant prayer. Within a month they saw the places on his right hand and left occupied by the two thieves in the crucifixion. The cup is an Old Testament image of a man's lot, or portion, as holding what of life God pours out for him.
Baptism is the necessary condition by which one can enjoy the privileges of the church.
We are able. They no doubt thought they were. They loved their Lord, as well as pre-eminence, and felt that they were willing to go with him through suffering. They, however, overestimated their strength. Ye shall drink indeed of my cup.