Philemon 1:15

‘For perhaps he was therefore parted (from you) for a season, that you might have him for ever,’

For while he would have liked to keep Onesimus, or have him back, he recognised the possibility that perhaps God had parted Onesimus from Philemon for a short so that he might then enjoy him for ever. It could therefore be that it would be right for Onesimus to remain with Philemon, whatever Paul’s desire, so that having been parted from him for a short time, he might have him permanently, ‘for ever’, as a dear brother in Christ, to be a companion to him in his old age. It may well be that Paul even saw Philemon as becoming almost a father to the boy, fulfilling Philemon’s desire for a son.

The thought of ‘having him for ever’ may mean that Paul had in mind the Old Testament custom of the Hebrew bondservant who chose to remain with his master ‘for ever’, rather than enjoying his freedom after seven years (Exodus 21:5-6).