“You do not know what you are asking. Are you able to drink the cup that I drink, or be baptized with the baptism that I am baptized with?”
James and John want a share in Christ's glory, to sit at the right and left hand of His throne at the consummation of all things. But instead of rebuking their "jealousy and selfish ambition" (James 3:16) Jesus invites them into glory by giving them its key, the Passion.
He invites them to share in this, to drink His cup of suffering and to live His baptism of death. Through this comes resurrection and triumphant life. But so easy to say, so hard to do! James and John, doubtless unwittingly, say they're able and they are, in the end. Christ's question becomes prophecy.
He asks the same thing of us. Perhaps this is helpful:
The mind, when purified by Christ’s Chalice is enabled to see spiritual visions. It begins to see the all-embracing Providence of God which is invisible to carnal minds, to see the law of corruption in everything corruptible, to see close to everyone a vast eternity, to see God in His great acts – in the creation and re-creation of the world. Earthly life seems to it a brief pilgrimage; the passing events of earthly life seem like dreams, and its blessings seem to he a fleeting illusion of the, eyes, a short-lived fatal allurement of the mind and heart.
To put it another way, "Whoever does not carry his cross and follow Me cannot be My disciple." (Lk 14:27) And again, "You cannot serve God and Mammon." (Mt. 6:24) By contrast, we should be like the "little child." (Mk 10:15)
May God bless us all in the endeavour.
LSP