There’s a good list of qualities here for Christians to cultivate: diligence, faith, moral excellence, knowledge, self-control, perseverance/patience, godliness, brotherly kindness, and love. I had first noted that this list seems to be in order of ascending importance, but I’m not so sure of that now.
On the other hand, Peter warns against lust, sensuality, willfulness, imprudence, greed, and arrogance/vanity.
He also warns of the liars/false prophets who will mock/exploit you.
Paul is wise, and his writings — while sometimes “hard to understand” — are Scripture (3:15-16). Well, that’s a noteworthy endorsement, is it not?
And speaking of noteworthy: Peter says flatly that, far from being a made-up story, Jesus Christ is a hard and fast fact (1:16-18).
Peter also promises that the Lord will come, and punish those who do not repent — but for Him one day is like a thousand years for us.
Note that there’s not a tight historical connection between I and II Peter in terms of recipients, purpose, etc. Note also that there’s a reference in II Peter 1:10 to “calling and election,” but note also that this and the following verse also suggest that our choices determine whether we will be provided an entrance “into the eternal kingdom.” And, finally, it’s also noteworthy that Peter confirms the Transfiguration, which he witnessed (II Peter 1:16-18).