Theophylact of Ohrid
Catena Aurea · Markusevangelium 10
And James and John, the sons of Zebedee, come unto him, saying, Master, we would that thou shouldest do for us whatsoever we shall desire. And he said unto them, What would ye that I should do for you? They said unto him, Grant unto us that we may sit, one on thy right hand, and the other on thy left hand, in thy glory. But Jesus said unto them, Ye know not what ye ask: can ye drink of the cup that I drink of? and be baptized with the baptism that I am baptized with? And they said unto him, We can. And Jesus said unto them, Ye shall indeed drink of the cup that I drink of; and with the baptism that I am baptized withal shall ye be baptized: But to sit on my right hand and on my left hand is not mine to give; but it shall be given to them for whom it is prepared.
But by the cup and baptism, He means the cross; the cup, that is, as being a potion by Him sweetly received, but baptism as the cause of the cleansing of our sins. And they answer Him, without understanding what He had said; wherefore it goes on: And they said unto him, We can; for they thought that He spoke of a visible cup, and of the baptism of which the Jews made use, that is, the washings before their meals.