John 21:19

19.Signifying by what death he should glorify God. This circumlocution is highly emphatic; for though the end held out to all believers ought to be, to glorify God both by their life and by their death, yet John intended to employ a remarkable commendation for adorning the death of those who, by their blood, seal the Gospel of Christ and glorify his name, as Paul teaches us, (Philippians 1:20.) It is now our duty to reap the fruit which the death of Peter has yielded; for it ought to be imputed to our indolence, if our faith be not confirmed by it, and if we do not keep the same object in view, that the glory of God may be displayed by us. If the Papists had considered this end in the death of the martyrs, that sacrilegious and detestable invention would never have entered into their minds, that their death contributes to appease the wrath of God, and to pay the ransom for our sins.

And when he had said this. Christ here explains what was the design of that prediction of a violent death. It was, that Peter might be prepared to endure it; as if he had said, “Since you must endure death by my example, follow your leader.” Again, that Peter may the more willingly obey God who calls him to the cross, Christ offers himself as a leader; for this is not a general exhortation by which he invites him to imitate himself, but he speaks only of the kind of death. Now, this single consideration greatly soothes all the bitterness that is in death, when the Son of God presents himself before our eyes with his blessed resurrection, which is our triumph over death.