Why does Paul make mention of the fact that he is writing with his own hand?
Philemon 1:19 (ESV)
19I, Paul, write this with my own hand: I will repay it to say nothing of your owing me even your own self.
Paul makes it clear that he is writing the letter in order to identify himself with Onesimus and confirm that he will honour his commitment to pay any debt.1 It is more likely that Paul wrote the entire letter himself rather than taking the pen from an amanuensis to write but one sentence.2
19 I, Paul, write this with my own hand: I will repay it to say nothing of your owing me even your own self.