Beloved, this is now my second letter to you. Both of them are reminders to stir you to wholesome thinking
This second epistle, beloved, I now write unto you; in [both] which I stir up your pure minds by way of remembrance: (1) The remedy against those wicked enemies, both of true doctrine and holiness, is to be sought for by the continual meditation of the writings of the prophets and apostles.
Peter calls this his second epistle to the same saints he had written before, addressing them as beloved because they are chosen and redeemed by Christ, sanctified by the Spirit, and sharers in the same faith as the apostles themselves.
AI summary
Both epistles serve one design: to put believers in remembrance of what they have heard but may not have retained. Ministers are the Lord's remembrancers, for even the purest minds grow dull and need constant refreshing; the best Christians stand in need of repeated stirring up to their duty.
AI summary