"Then the mother of Zebedee's sons came to Him [Jesus] with her sons, kneeling down and asking something from Him. And He said to her, 'What do you wish?' She said to Him, 'Grant that these two sons of mine may sit, one on Your right hand and the other on the left, in Your kingdom.' But Jesus answered and said, 'You do not know what you ask. Are you able to drink the cup that I am about to drink, and be baptized with the baptism that I am baptized with?' They said to Him, 'We are able.' So He said to them, 'You will indeed drink My cup, and be baptized with the baptism that I am baptized with; but to sit on My right hand and on My left is not Mine to give, but it is for those for whom it is prepared by My Father'" (Matt. 20:20-23).
James and John ask this question through the lips of their mother, perhaps thinking that Jesus would be more likely to grant the request coming from her (e.g., I Kings 2:19,20). Her bowing down before Jesus was probably out of respect for Him as a coming ruler and not as worship of a divine being.
"Teacher, we want You to do for us whatever we ask" (Mark 10:35). They indicate that they are ashamed of their selfish request by desiring Jesus to grant it without hearing it. Jesus did not promise to grant their wish, but He does ask them to specify what it was (not because He didn't know, but so their self-seeking could be clearly exposed and then properly rebuked).
"Grant that these two sons of mine may sit, one on Your right hand and the other on the left, in Your kingdom" (Matt. 20:21). The greatest honor was to sit at the right hand of a king; the second best honor was to sit at his left side. In 19:28, Jesus had spoken about the thrones that the apostles would occupy. Evidently the apostles understood Jesus to be speaking literally, and thus this request is intended to distinguish their thrones as preeminent among the twelve.
Jesus replied - "You do not know what you ask." This is certainly the case in many petitions today that are spoken to God. In a similar fashion as James and John, our worldly ambitions, selfish ways, and ignorance prompts us to make requests that are not appropriate.
"Are you able to drink the cup that I am about to drink, and be baptized with the baptism that I am baptized with?" (Matt. 20:22). To the Hebrews, the word "cup" was understood to mean "one's assigned portion" (cf. Psa. 11:6; Matt. 26:39,42; John 18:11). On this occasion, it was used as a symbol of Jesus' suffering, which would be culminated at the cross (i.e., His "assigned portion").
"Baptism" means the same thing here as it does everywhere else in the New Testament--"to immerse, to submerge, to overwhelm." The Greek word for baptism does not inherently specify the element in which the immersion is to occur. The Great Commission requires an immersion in water for the remission of sins, preceded by a penitent faith in Christ (cf. Matt. 28:19,20; John 8:24; Acts 2:38; 10:47). In this passage, the element implied is not water but suffering. Jesus is graphically portraying His suffering as a baptism; that is, He would be immersed, submerged, and overwhelmed by the physical and spiritual suffering He would soon be subjected to on the cross. The agony of crucifixion wouldn't just be "sprinkled" or "poured" upon Him, but He would be immersed into it.
Some commentators make a distinction between the "cup" and "baptism" by stating that the former refers to inward spiritual suffering and the latter to outer persecution. It should be noted that the present tense is used here which indicates that even then suffering and persecution were being experienced.
"We are able" - Their response to Jesus is confident and accurate. They believed they were courageous and able to pledge themselves to whatever "cup" Jesus was referring to. They probably thought He was referring to some physical battle which would make His physical kingdom possible.
"You will indeed drink My cup, and be baptized with the baptism that I am baptized with" (Matt. 20:23). James drank the cup by suffering martyrdom at the hands of Herod Agrippa. He was the first apostle to die for the faith (cf. Acts 12:2). John outlived all of the other apostles and was the only one to die of natural causes. However, he certainly drank the cup via the years of suffering and persecution he endured (cf. Rev. 1:9).
"But to sit on My right hand and on My left is not Mine to give, but it is for those for whom it is prepared by My Father" - Jesus knew that those who were faithful to Him would partake of the sufferings and hardships of persecution (cf. II Tim. 3:12), but they wouldn't necessarily be given the chief seats. Jesus loved John in particular (cf. John 21:20-24), but the chief seats would not be distributed according to personal favoritism but according to the will of the Father.