For perhaps he therefore departed for a season - Perhaps on this account, or for this reason - διὰ τοῦτο dia touto - he left you for a little time. Greek, “for an hour” - πρὸς ὥραν pros hōran. The meaning is, that it was possible that this was permitted in the Providence of God in order that Onesimus might be brought under the influence of the gospel, and be far more serviceable to Philemon as a Christian, than he could have been in his former relation to him. What appeared to Philemon, therefore, to be a calamity, and what seemed to him to be wrong on the part of Onesimus, might have been permitted to occur in order that he might receive a higher benefit. Such things are not uncommon in human affairs.
That thou shouldest receive him for ever - That is, in the higher relation of a Christian friend and brother; that he might be united to thee in eternal affection; that he might not only be with thee in a far more endearing relation during the present life than he was before, but in the bonds of love in a world that shall never end.