A.T. Robertson 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)

Perhaps (ταχα). Old adverb, in N.T. only here and Ro 5:7.

That thou shouldst have him (ινα αυτον απεχηις). Final clause with ινα and present active subjunctive of απεχω, to have back, "that thou might keep on having him back."

For ever (αιωνιον). "Eternal," here and hereafter. Surely a noble thing for Paul to say and a word that would touch the best in Philemon.