Although 1 Peter is a short letter, it touches on various doctrines and has much to say about Christian life and duties. It is not surprising that different readers have found it to have different principal themes. For example, it has been characterised as a letter of separation, of suffering and persecution, of suffering and glory, of hope, of pilgrimage, of courage, and as a letter dealing with the true grace of God.
The same great doctrines, as in St. Paul’s epistles, are here applied to same practical purposes. And this epistle is remarkable for the sweetness, gentleness, and humble love, with which it is written. It gives a short, and yet a very clear summary, both of the consolations and the instructions needful for the encouragement and direction of a Christian in his journey to heaven, raising his thoughts and desires to that happiness, and strengthening him against all opposition in the way, both from corruption within, and temptations and afflictions without. Matthew Henry