When the mother of James and John asks for her sons to sit on Jesus’s right and left side when the kingdom comes, Jesus says they are not able to “drink the cup” he is about to drink from (Matt 20:22). More or less, Jesus tells the mother and the two sons (the verbs are all second plural) do not know what they are asking!
“Drinking the cup” is a clear reference to the suffering from the three passion predictions (20:17-19). Drinking a cup is a common metaphor for the wrath of God in the Old Testament (Jer 25:15-16; Psalm 75:8; Isaiah 51:17-23; PsSol 8:14).
Isaiah 51:18, 22(ESV) Wake yourself, wake yourself, stand up, O Jerusalem, you who have drunk from the hand of the Lord the cup of his wrath, who have drunk to the dregs the bowl, the cup of staggering. 22 Thus says your Lord, the Lord, your God who pleads the cause of his people: “Behold, I have taken from your hand the cup of staggering; the bowl of my wrath you shall drink no more.
Psalms of Solomon 8:14 Because of this God mixed them (a drink) of a wavering spirit, and gave them a cup of undiluted wine to make them drunk.
When Jesus prays in the Garden of Gethsemane he asks for the “cup he is about to drink” to be taken from him, an indication he is about to face the wrath of God as he punishes sin.
James and John claim they can suffer and die along with Jesus (20:22b). This bold assertion is like Peter’s claim at the last supper that he is able to suffer and die with Jesus (Matthew 26:33). However, when the time comes to suffer and die with Jesus, James and John fall asleep along with Peter. The “sons of Zebedee can do nothing but sleep while Jesus wrestles with drinking his ποτήριον” (Davies and Allison, Matthew, 3:89). That they think they can suffer in the same way Jesus will indicates they do not really understand what will happen when they arrive in Jerusalem.
In response, Jesus predicts James and John will “drink that cup,” but as for seating in the kingdom of heaven, that is prepared by the Father (20:23). James is the first martyr. He is the first of the disciples to be executed for his faith (Acts 12:1). James was beheaded by Herod Agrippa I (not to be confused with Herod Agrippa II in Acts 26). John, on the other hand, lived a very long life, probably into the 90s A.D. It is possible he was quite young during the ministry of Jesus, maybe even a young teen, and lived a long life, often persecuted for his faith (see Ireneaus, Adv. Haer, 2.22).
The reaction of the other disciples: They were indignant! (20:24). It is possible their mother made this request in public, but most think they took Jesus aside to ask him in private. The verb ἀγανακτέω is to be angry at “what is assumed to be wrong” (BDAG); to “be vexed” (BrillDAG; the word is used in medical texts for literal irritation). Later in Matthew the Pharisees will be indignant when the disciples are shouting “hosanna” as Jesus rides the donkey into Jerusalem (21:15). The was used for the response of a disciple who thinks the woman who anoints Jesus in Bethany is wasting money which could have been given to the poor (Matt 26:8).
This bold request from the mother of the sons of Zebedee indicates these two inner circle disciples have not fully understood Jesus’s predictions that he is going to suffer and die in Jerusalem. Although they fully understand Jesus is the Messiah, they do not yet understand the messiah’s mission is to serve as “a ransom for many.”