John 21:18

“(Hom. lxxxvii) Our Lord having made Peter declare his love, informs him of his future martyrdom; an intimation to us how we should love: Verily, verily, I say unto thee, When thou wast young, thou girdedst thyself, and walkedst whither thou wouldest. He reminds him of his former life, because, whereas in worldly matters a young man has powers, an old man none; in spiritual things, on the contrary, virtue is brighter, manliness stronger, in old age; age is no hindrance to grace. Peter had all along desired to share Christ’s dangers; so Christ tells him, Be of good cheer; I will fulfil thy desire in such a way, that what thou hast not suffered when young, thou shalt suffer when old: But when thou art old. Whence it appears, that he was then neither a young nor an old man, but in the prime of life.”

“(Hom. lxxxviii) He says, Whither thou wouldest not, with reference to the natural reluctance of the soul to be separated from the body; an instinct implanted by God to prevent men putting an end to themselves. Then raising the subject, the Evangelist says, This spake He, signifying by what death he should glorify God: not, should die: he expresses himself so, to intimate that to suffer for Christ was the glory of the sufferer. (non occ.). But unless the mind is persuaded that He is very God, the sight of Him can in no way enable us to endure death. Wherefore the death of the saints is certainty of divine glory.”

“(Tract. cxxiii. 5) That is, shalt be crucified. And to come to this end, Another shall gird thee, and carry thee whither thou wouldest not. First He said what would come to pass, secondly, how it would come to pass. For it was not when crucified, but when about to be crucified, that he was led whither he would not. He wished to be released from the body, and be with Christ; but, if it were possible, he wished to attain to eternal life without the pains of death: to which he went against his will, but conquered by the force of his will, and triumphing over the human feeling, so natural a one, that even old age could not deprive Peter of it. But whatever be the pain of death, it ought to be conquered by the strength of love for Him, Who being our life, voluntarily also underwent death for us. For if there is no pain in death, or very little, the glory of martyrdom would not be great.”