Jesus answers Peter's question about John with a question of His own. Peter had just heard that in old age another would gird him "and carry thee whither thou wouldest not" (John 21:18), and he wanted to know what lay ahead for his friend. Barnes offers more than one possible reason for Peter's question. Matthew Henry allows that it may have been "concern for John, and kindness to him," or uneasiness about his own sufferings. Either way, Jesus' question presses Peter to see that John's future rested on the Lord's will ("If I will"), not on Peter's knowing it. Henry also gives the reading of those who take Jesus' words as a rebuke to Peter's curiosity: "It is nothing to thee, when or where, or how, John must die."

The text records no reply from Peter. Jesus closes the matter Himself in the same breath: "follow thou me" (John 21:22), repeating the call He had just given in John 21:19. The next verse shows how His words were misheard: "Then went this saying abroad among the brethren, that that disciple should not die" (John 21:23). The writer corrects the rumor by repeating exactly what Jesus said, and then names himself as "the disciple which testifieth of these things" (John 21:24).

"Tarry" translates the Greek menein, to remain. Barnes reads "That he tarry" simply as "That he live," and he points to the same idea of remaining alive in Philippians 1:24-25 ("abide") and 1 Corinthians 15:6 ("remain unto this present").

Commentators read "till I come" differently. Gill takes it not of Christ's final coming but of His coming "in his power" to judge the Jewish nation in the destruction of Jerusalem and the temple by the Romans. Barnes takes it as a supposition: even if Jesus willed that John should not die at all, that was not Peter's concern. Either way, the point of the question stands.

In the Greek, Jesus' last words begin with an added "you" (su akolouthei moi, "you, follow me"), which the ESV brings out: "You follow me!"

Jesus had just restored Peter with three questions about love and the charge to feed His sheep (John 21:15-17), and then told him he would "glorify God" by his death (John 21:19). Peter's glance at John was natural. But Jesus' answer shows that He is the one who assigns each disciple's path and each disciple's end. Both men's lives sat inside the words "If I will." Barnes draws from this that Jesus cares for all His disciples, so we need not be anxious about them, and that we should accept whatever He calls us to without envying the lot of others.

The last command Peter hears in this Gospel is the same one he first heard by the sea of Galilee: "Follow me" (Matthew 4:19; John 21:22). Gill sums it up: "it becomes the saints to mind their duty in following Christ, and not concern themselves in things that do not belong to them."