Matthew 20:23

‘He says to them, “You will indeed drink my cup. But to sit on my right hand, and on my left hand, is not mine to give, but it is for those for whom it has been prepared of my Father.” '

All this Jesus knows. But as He looks at them, He loves them, and He is indeed aware of what they must suffer for His Name's sake. So instead of pointing out that they are mistaken and have no idea what they are promising, He descends to a certain extent to their level and acknowledges that they will indeed drink of His cup, at least to some extent. For both will in future be called on to suffer in the cause of Christ. Both will shortly endure regular imprisonment and beatings (Acts 4:3; Acts 5:18; Acts 5:40), and James will later be beheaded by Herod Agrippa 1 (Acts 12:2), while John will suffer in other ways, as will all the disciples. It would be a bold person indeed who would suggest that John would pass through the tribulations of the first century AD and remain unscathed, and the traditions of John's sufferings in the mines on the Isle of Patmos may well contain some truth (compare Revelation 1:9).

This kind of enigmatic reply by Jesus is His regular way of avoiding going into detail over things about which the disciples are mistaken, (compare also Luke 22:38; Acts 1:6), but concerning which there is no point in giving an immediate explanation. He knew that there was much that they still had to learn and appreciate before they could be taught more fully.

But then He points out that, whatever they may feel themselves capable of, the privilege of being those closest to Him in authority is not within His gift. It is for those for whom the Father has prepared it. Initially at least we may well think that Acts reveals that it was Peter and Paul who were allocated these positions, with John taking one up once they were dead. But they did not see themselves in that way. And that was in a future that was at present not yet known. Jesus' point, however, is that it is God Who will choose the future church leadership, not man, not even Himself. God prepares each man for the task that he has to do (John 15:16; Acts 13:2; Galatians 1:15).