Paul was so confident in his Epistle to Philemon that the latter would grant his major request because

Paul was confident in his Epistle to Philemon because he appealed to him not only on the basis of Onesimus being his slave but as a brother in Christ. He recognized Philemon's faith in Christ and appealed to him to forgive Onesimus and accept him back as a brother in Christ, rather than as a slave. Paul also promised to repay any wrong Onesimus may have done to Philemon, thus demonstrating his willingness to take responsibility for Onesimus' actions. This approach showed Paul's understanding of the Christian faith as being based on forgiveness, reconciliation, and brotherhood in Christ, which he believed Philemon would also uphold.