Jamieson, Fausset and Brown on Philemon 1:19

19. with mine own hand--not employing an amanuensis, as in other Epistles: a special compliment to Philemon which he ought to show his appreciation of by granting Paul's request. Contrast Col 4:18, which shows that the Epistle to the Colossian Church, accompanying this Epistle, had only its closing "salutation" written by Paul's own hand.

albeit, &c.--literally, "that I may not say ... not to say," &c.

thou owest ... even thine own self--not merely thy possessions. For to my instrumentality thou owest thy salvation. So the debt which "he oweth thee" being transferred upon me (I making myself responsible for it) is cancelled.