Expositor's Bible Commentary Commentary Philemon 1:15

"For perhaps he was therefore parted [from thee] for a season, that thou shouldest have him for ever;" — Philemon 1:15 (ASV)

The contrast between “for a time” and “forever” shows Paul’s conviction that the hand of God was at work in the whole situation. It also shows his tact: instead of bluntly referring to Onesimus as a runaway, he speaks of his temporary separation from Philemon as a prelude to permanent reunion with him.