Onesimus had known the Apostle well in the old days when Paul visited at the house of his master Philemon, who seems to have been a man of importance. His house was large enough to admit of a church assembling in it, and to accommodate the Apostle and his traveling companions when they came to the city. Apphia, his wife, was also a Christian, and Archippus, their son, was engaged in some kind of Christian work in connection with the infant Christian community which they were nursing. Compare Phm 1:1-2 with Col 4:17. It is beautiful to observe the Apostle’s humility in associating these obscure people with himself as fellow-workers.
Onesimus had been a runaway slave, and fleeing to Rome, had been converted by the ministry of Paul-whom I have begotten in my bonds. The converted slave had become very dear and useful to his benefactor, Phm 1:12-13. The Apostle now sends him back to his former owner with this letter, pleading that he be once more received into the household of Philemon.