Calvin's Commentaries, Vol. 45: Catholic Epistles, tr. by John King, [1847-50], at sacred-texts.com
The doubts respecting this Epistle mentioned by Eusebius, ought not to keep us from reading it. For if the doubts rested on the authority of men, whose names he does not give, we ought to pay no more regard to it than to that of unknown men. And he afterwards adds, that it was everywhere received without any dispute. What Jerome writes influences me somewhat more, that some, induced by a difference in the style, did not think that Peter was the author. For though some affinity may be traced, yet I confess that there is that manifest difference which distinguishes different writers. There are also other probable conjectures by which we may conclude that it was written by another rather than by Peter. At the same time, according to the consent of all, it has nothing unworthy of Peter, as it shews everywhere the power and the grace of an apostolic spirit. If it be received as canonical, we must allow Peter to be the author, since it has his name inscribed, and he also testifies that he had lived with Christ: and it would have been a fiction unworthy of a minister of Christ, to have personated another individual. So then I conclude, that if the Epistle be deemed worthy of credit, it must have proceeded from Peter; not that he himself wrote it, but that some one of his disciples set forth in writing, by his command, those things which the necessity of the times required. For it is probable that he was now in extreme old age, for he says, that he was near his end. And it may have been that at the request of the godly, he allowed this testimony of his mind to be recorded shortly before his death, because it might have somewhat availed, when he was dead, to support the good, and to repress the wicked. Doubtless, as in every part of the Epistle the majesty of the Spirit of Christ appears, to repudiate it is what I dread, though I do not here recognize the language of Peter. But since it is not quite evident as to the author, I shall allow myself the liberty of using the word Peter or Apostle indiscriminately.
I shall now come to the argument, which may be briefly stated.
The design is to shew, that those who have once professed the true faith of Christ, ought to respond to their calling to the last. After having then extolled, in high terms, the grace of God, he recommends to them holiness of life, because God usually punishes in hypocrites a false profession of his name, with dreadful blindness, and on the other hand he increases his gifts to those who truly and from the heart embrace the doctrine of religion. He, therefore, exhorts them to prove their calling by a holy life. And, to give a greater weight to his admonitions, he says that he is already near his end, and at the same time, excuses himself that he so often repeated the same things, his object being that they who should remain alive on the earth after his death, might have what he, when alive, wrote, more deeply fixed in their minds.
And as the foundation of true religion is the certainty or the truth of the gospel, he shews, first, how indubitable is its truth by this fact, — that he himself had been an eyewitness of all things which it contains, and especially that he had heard Christ proclaimed from heaven to be the Son of God; and, in the second place, it was God's will that it should be borne witness to, and approved by the oracles of the prophets.
He, however, predicts, at the same time, that danger was approaching from false teachers, who would spread impious inventions, as well as from the despisers of God, who would mock all religion; and he did this, that the faithful might learn to be watchful, and that they might be fortified. And he seems to have spoken thus designedly, lest they expected that the course of truth in the kingdom of Christ would be tranquil and peaceable, and free from all contention. He afterwards, as on a tablet, describes the character and manners of those who would, by their corruptions, pollute Christianity. But the description which he presents, especially suits the present age, as it will be more evident by a comparison. For he especially draws his pen against Lucianic men, who abandon themselves to every wickedness, and take a profane license to shew contempt to God, yea, and treat with ridicule the hope of a better life; and at this day we see that the world is everywhere full of such rabble.
He further exhorts the faithful, not only to look always for the coming of Christ with suspended and expectant minds, but also to regard that day as present before their eyes, and in the meantime to keep themselves unpolluted for the Lord: in which doctrine he makes Paul as his associate and approver; and to defend his writings from the calumnies of the ungodly, he severely reproves all those who pervert them.