Peter proceeded to address the situation of Christians working under the authority of others. [source][source][source]
"The unusual fact, unnoticed by most Bible readers, is that he [1], along with Paul ( 1 Corinthians 7:21; Ephesians 6:5-8; Colossians 3:22-25; 1 Timothy 6:1-2; Titus 2:9-10) and later Christian writers (Did. 4:11; Barn19:7), addresses slaves at all, for Jewish and Stoic duty codes (which in many respects this code in1Peter, as well as those in Ephesians and Colossians , resembles) put no such moral demands on slaves, only on masters. [source][source][source]
"The reason for this difference between1Peter and other moral codes of his time is simple. For society at large slaves were not full persons and thus did not have moral responsibility. For the church slaves were full and equal persons, and thus quite appropriately addressed as such. The church never addressed the institution of slavery in society, for it was outside its province-society in that day did not claim to be representative, and certainly not representative of Christians, concepts that arrived with the Enlightenment-but it did address the situation in the church, where no social distinctions were to be allowed, for all were brothers and sisters ( Galatians 3:28; 1 Corinthians 12:13; Colossians 3:11; Philemon 1:16), however shocking that was to society at large." [2][source]
Peter evidently addressed servants but not masters because he addressed a social situation in which some of his readers were household servants but few, if any, were masters. [3][source]