2 Peter 3:11

The apostle, having instructed them in the doctrine of Christ's second coming, I. Takes occasion thence to exhort them to purity and godliness in their whole conversation: all the truths which are revealed in scripture should be improved for our advancement in practical godliness: this is the effect that knowledge must produce, or we are never the better for it. If you know these things, happy are you if you do them. Seeing all these things must be dissolved, how holy should we be, that are assured of it, departing from and dying to sin, that has so corrupted and defiled all the visible creation that there is an absolute need of its dissolution! All that was made for man's use is subject to vanity by man's sin: and if the sin of man has brought the visible heavens, and the elements and earth, under a curse, from which they cannot be freed without being dissolved, what an abominable evil is sin, and how much to be hated by us! And, inasmuch as this dissolution is in order to their being restored to their primitive beauty and excellency, how pure and holy should we be, in order to our being fit for the new heaven and new earth, wherein dwelleth righteousness! It is a very exact and universal holiness that he exhorts to, not resting in any lower measure or degree, but labouring to be eminent beyond what is commonly attained - holy in God's house and in our own,…

— Matthew Henry's Concise Commentary (public domain)

Your duty, seeing that this is so, is to be ever eagerly expecting the day of God. then--Some oldest manuscripts substitute "thus" for "then": a happy refutation of the "thus" of the scoffers, Pe2 3:4 (English Version, "As they were," Greek, "thus"). shall be--Greek, "are being (in God's appointment, soon to be fulfilled) dissolved"; the present tense implying the certainty as though it were actually present. what manner of men--exclamatory. How watchful, prayerful, zealous! to be--not the mere Greek substantive verb of existence (einai), but (huparchein) denoting a state or condition in which one is supposed to be [TITTMANN]. What holy men ye ought to be found to be, when the event comes! This is "the holy commandment" mentioned in Pe2 3:2. conversation . . . godliness--Greek, plural: behaviors (towards men), godlinesses (or pieties towards God) in their manifold modes of manifestation.

— Jamieson-Fausset-Brown Commentary (public domain)