John Calvin Commentary 2 Peter 3:17

"Ye therefore, beloved, knowing [these things] beforehand, beware lest, being carried away with the error of the wicked, ye fall from your own stedfastness." — 2 Peter 3:17 (ASV)

Ye, therefore, beloved. After having shown the faithful the dangers they were to beware of, he now concludes by admonishing them to be wise. But he shows that there was a need to be watchful, so that they would not be overwhelmed. And, undoubtedly, the cunning of our enemy, the many and various treacheries he employs against us, and the frivolous objections of ungodly men, leave no room for security. Therefore, vigilance must be exercised, so that the devices of Satan and of the wicked do not succeed in ensnaring us. However, it seems that we stand on slippery ground, and the certainty of our salvation hangs, as it were, by a thread, since he declares to the faithful that they ought to take care not to fall from their own steadfastness.

What, then, will become of us, if we are exposed to the danger of falling? To this I answer, that this exhortation, and others like it, are by no means intended to shake the firmness of that faith which rests on God, but to correct the sluggishness of our flesh. If anyone wishes to see more on this subject, they should read what has been said on 1 Corinthians 10.

The meaning is this: that as long as we are in the flesh, our sluggishness must be roused, and that this is appropriately done by having our weakness and the variety of dangers that surround us placed before our eyes; but that the confidence that rests on God's promises ought not to be shaken by this.