Commenting on 1 Peter 1:1, the Roman Catholic Bible translator Rupert Storr says that the apostle Peter wrote his first letter to Christians and that chapters 1Pe 1:3 to 4:11 are a sermon addressed to newly baptized ones.
... And “finally, all of you be like-minded, showing fellow feeling, exercising brotherly love, tenderly affectionate, humble in mind, not paying back injury for injury or reviling for reviling, but, to the contrary, bestowing a blessing, because you were called to this course, so that you might inherit a blessing.” (1 Pet. 3:8, 9)