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.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Tract. cxxiii. 5