Philemon 1:16
Not now as a servant, but above a servant, a brother beloved, specially to me, but how much more unto thee, both in the flesh, and in the Lord? Not now as a servant, but above a servant, a brother beloved, specially to me, but how much more unto thee, both in the flesh, and in the Lord?
Paul's appeal belongs to the time of his arrival and imprisonment in Rome described in Acts 28:11-31. It was made when slaveholding was an established institution throughout the Roman empire, with both masters and slaves found in most churches, and where in cities slaves often greatly outnumbered the free population and were kept in subjection by laws of terrible severity. A wealthy Roman often owned hundreds of slaves of every rank, nation, and accomplishment, with full control over the souls and bodies of these helpless beings to inflict any suffering he chose, so that if one in retaliation or self-defense raised a hand against his owner the whole family of the offender might be sacrificed, and the slightest mistake, accident, or carelessness was often punished without mercy. Some masters more humane than others were more indulgent toward their servants, but the vast majority, given up to lust, passion, and appetite, made their slaves the victims of caprice and tyranny, and the tendency of the whole system was hopelessly degrading. In that setting the verse shows the influence of the gospel upon the relation between master and servant.
Not as a servant but above a servant means that Onesimus, though formerly Philemon's slave and returning as a servant, had been changed by conversion and was no longer to be regarded only as a slave but as more than a slave. His new standing made him a beloved brother in Christ and in the faith, a member of Christ's body and a fellow heir with his master in the blessings of God and the privileges of the gospel. Philemon was therefore to receive him with affection and brotherly love and treatment, taking him as his own child. The affection shown to him was to be such that he would choose to stay with his former master willingly rather than serve under compulsion.
Paul's bond with Onesimus as fellow believers made any punishment of Onesimus feel to Paul like punishment of himself. Paul wanted to keep Onesimus to serve him in prison in Philemon's place, as Philemon himself would have served, but he would do so only if Philemon of his own accord set the slave free.