38 Grk “I wrote” Here ἔγραψα (egrapsa) is functioning as an epistolary aorist. Paul puts it in the past tense because from Philemon’s perspective when he reads the letter it will, of course, already have been written.
39 The phrase “this letter” does not appear in the Greek text, but is supplied in the English translation to clarify the meaning.
40 With my own hand. Paul may have considered this letter so delicate that he wrote the letter himself as opposed to using an amanuensis or secretary.
41 The statement you owe me your very self means that Paul was responsible for some sort of blessing in the life of Philemon; though a monetary idea may be in mind, it is perhaps better to understand Paul as referring to the spiritual truth (i.e., the gospel) he had taught Philemon.

In other versions

I, Paul, write this with my own hand: I will repay it—to say nothing of your owing me even your own self.

I, Paul, am writing this with my own hand. I will pay it back—not to mention that you owe me your very self.

I, Paul, write this with my own hand: I will repay it—not to mention to you that you owe me even your very self.

I, Paul, write this with my own hand: I will repay it. And I won’t mention that you owe me your very soul!

I, Paul, write this with my own hand: I will pay it back, lest I mention to you that you owe me even your very self besides.

I Paul have written it with mine own hand, I will repay it: albeit I do not say to thee how thou owest unto me even thine own self besides.

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