The idea of a permanent return could allude to the fact that Onesimus, being a Christian, would now faithfully serve his master and not run away again. More likely, it is a reference to the eternal fellowship that Onesimus and Philemon would enjoy seeing as they both belonged to Christ. A new relationship that transcends earthly relationships.1
15 For this perhaps is why he was parted from you for a while, that you might have him back forever,