Theophylact of Ohrid — as excerpted in the Catena Aurea on Mark 10:35-40

“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.”