John 21:18
Verily, verily, I say unto thee, When thou wast young, thou girdedst thyself, and walkedst whither thou wouldest: but when thou shalt be old, thou shalt stretch forth thy hands, and another shall gird thee, and carry thee whither thou wouldest not.
After restoring Peter and entrusting him with the care of the flock, Jesus told him privately that when he was young he girded himself and went where he chose, but when old and weakened he would stretch out his hands to be bound by another and carried where he did not wish to go, meaning he would die by crucifixion upon a cross to glorify God. After a long and useful life he would indeed follow his Lord as he had once promised, fulfilling the word that he could not follow then but would follow afterward, and Jesus then renewed the command to follow Him. Peter received the revelation without fear, counting it an honor to suffer any death for his Lord as his Master had suffered, and at last yielded his life for the gospel, asking at his own request to be crucified with his head downward as unworthy to suffer in exactly the same way, in humility and lasting remorse for his denial. Being ready for such a sacrificial death required no longer knowing Christ merely as a man and heaven-sent teacher but loving Him as God until He became all in all, which gave Peter noble courage to preach a crucified, risen, and ascended Saviour, so that when he lay in prison bound between two soldiers he remembered the prediction and knew the time to die for his faith was near. The command to follow belongs to everyone in individual discipleship, not looking curiously at what another such as John will do nor at another's defects, but keeping the eye single to God's glory, while Peter's long course of intimate acquaintance, gifts, and influence even into old age yet ending in dissembling at Antioch where Paul withstood him stands as a solemn warning that even the best left to themselves will blunder and must depend daily on Christ alone.
Prediction of Peter's Death
These words were spoken privately to Peter in Galilee after the resurrection, in sympathy after restoring him and appointing him to care for the flock, opening his future to him to strengthen him for the final test of his faith. After living a long and useful life, when old age weakened his strength and age told upon him, Peter would indeed follow his Lord as he had earlier promised, fulfilling the earlier word that he could not follow then but would follow afterward.
The verse contrasts Peter's youth, when he girded himself and walked where he chose with freedom to go as he would, with his old age, when he would lose control, be bound by another, and be taken where he did not wish to go and would not naturally go. It states explicitly both the fact and the manner of his death, for the stretching forth of his hands means he would die by crucifixion upon a cross, with his hands stretched upon it. By that death of crucifixion for his faith he would glorify God. After giving this revelation Jesus renewed the call and command to Peter to follow Him.
Following Christ to Martyrdom
Peter received the disclosure of his coming death without fear, and was willing to suffer any death for his Lord, counting it an honor to die as his Master had died, and he did in the end yield up his life for the gospel. When at last he was brought to the cross it was at his own request that he was crucified with his head downward, because he counted it too great an honor to suffer in exactly the same way as his Master and felt himself unworthy to do so. That request showed humility and lasting remorse for having denied Christ. To be made ready to follow his Lord in such a sacrificial death he had to cease to know Christ after the flesh as merely a man and heaven-sent teacher, and to love Him as God, with Christ becoming all in all to him, and this prepared him to share in his Lord's mission of sacrifice.
After his reinstatement following his denial he was not intimidated by the death foretold for him, but faced danger with noble courage and boldness in preaching a crucified, risen, and ascended Saviour. When he lay in prison between two soldiers, bound with two chains and awaiting his appointed execution, he remembered the prediction that when old he would be bound and carried where he would not naturally go, in contrast to his youth when he girded himself and walked where he chose. He believed the time had come to give up his life for Christ, knowing that suffering for his faith was near and that he would soon die.
The command to follow is not for Peter alone but for all, for each person's work is to follow Christ in an individual discipleship. No one is to be curious about what another person such as John will do, nor to look at another's defects of character or course, but each is to keep the eye single to the glory of God by letting the world go out of reckoning and bringing eternal realities in. Christ's restoration of Peter opened a long course of service in which Peter gained intimate acquaintance with Christ, knowledge of His pure straightforward practice of principle, instruction, gifts, knowledge, and great influence in preaching and teaching the Word into old age. Yet even after all that he could still dissemble and evade gospel principles for fear of man and to gain esteem, wavering and being two-sided at Antioch where Paul had to withstand him face to face. This shows that even the best of men left to themselves will make grave blunders, and that the higher the position to dictate and control the more mischief is done when the way of the Lord is not carefully followed, so his failure is recorded that others may profit by it as a solemn warning to men in high places not to fail in integrity but to keep close to principle with a sense of personal helplessness and daily dependence on the grace of Christ alone.