The book of Philemon relates an interesting event in Paul's life in which he calls upon Philemon's sense of gratitude and obligation to him. In verse 8, Paul says he could use his authority to order Philemon to accept the slave Onesimus back, charging any debt he owed Philemon to Paul. However, he appeals to him through other means. In verse 19, he delivers a double-barreled proposition. First, Paul himself writes in his own hand that he will repay any of Onesimus' indebtedness, putting Philemon in greater-than-normal obligation. Then, Paul reminds him that he owes Paul his very life spiritually. He implies that Philemon's spiritual indebtedness to him should more than cover any material debt Onesimus owed to Philemon.
Therefore, Paul suggests that Philemon charge it to his account. What Paul did for Onesimus reflects in a small way what Christ did for us. As Paul laid himself out for Onesimus, Christ did for us in a much greater way to pay our spiritual indebtedness and set us free. As Paul claims Philemon's indebtedness to him, so Christ claims our indebtedness to Him.
John W. Ritenbaugh
The Elements of Motivation (Part Four): Obligation