In his first letter Peter feeds Christ’s sheep by instructing them how to deal with persecution from outside the church; in this second letter he teaches them how to deal with false teachers and evildoers who have come into the church.
This epistle clearly is connected with the former epistle of Peter. The apostle having stated the blessings to which God has called Christians, exhorts those who had received these precious gifts, to endeavour to improve in graces and virtues. They are urged to this from the wickedness of false teachers. They are guarded against impostors and scoffers, by disproving their false assertions, ch. 3:1-7: and by showing why the great day of Christ’s coming was delayed, with a description of its awful circumstances and consequences; and suitable exhortations to diligence and holiness are given.Matthew Henry