Rome to get free from Philemon his master (Col 4:9).

"A Phrygian slave was one of the lowest known types to be
found in the Roman world, displaying all the worst features of
character which the servile condition developed. Onesimus had
proved no exception. He ran away from his master, and, as Paul
thought probable (verses 18,19), not without helping himself to a
share of his master's possessions. By the help of what he had
stolen, and by the cleverness which afterwards made him so
helpful to Paul, he made his way to Rome, naturally drawn to the
great centre, and prompted both by a desire to hide himself and
by a youthful yearning to see the utmost the world could show of
glory and of vice.

"But whether feeling his loneliness, or wearied with a
life of vice, or impoverished and reduced to want, or seized with
a fear of detection, he made his way to Paul, or unbosomed
himself to some Asiatic he saw on the street. And as he stepped
out of the coarse debauchery and profanity of the crowded resorts
of the metropolis into the room hallowed by the presence of Paul,
he saw the foulness of the one life and the beauty of the other,
and was persuaded to accept the gospel he had so often heard in
his master's house.

"How long he remained with Paul does not appear, but it
was long enough to impress on the Apostle's mind that this slave
was no common man. Paul had devoted and active friends by him,
but this slave, trained to watch his master's wants and to
execute promptly all that was entrusted to him, became almost
indispensable to the Apostle. But to retain him, he feels, would