(a) St. Paul's letter to Philemon is an appeal to forgive his erstwhile slave, Onesimus and take him back. Onesimus had wronged his master and escaped. In his self imposed exile, he had come in contact with Paul (imprisoned in Rome) and had become a convert. He became closely attached to Paul by rendering useful service to him. Paul, therefore, sent him back to his master with a letter of appeal with the love of Christ. Paul began by congratulating Philemon on his love and devotion in the service of God, pointing out his immense joy for Philemon's goodness to the saints in the Church.
Paul claimed that, although as his mentor and benefactor, he had a right to command, but for God's sake, he preferred to appeal to Philemon's good sense, and urged him to take back Onesimus, not so much as a slave, but more importantly, as a Christian brother. Onesimus had formerly, by his action, been useless to Philemon so that by becoming a convert, he might become more useful and worthy to be taken back.
Paul said that he would have preferred to retain Onesimus, but the decision must be taken by Philemon himself. If Onesimus had owed him anything or made him suffer any financial losses, he should charge Paul's account; he would surely pay it during his next visit. He concluded by asking Philemon to prepare a guest house for him in readiness for his next visit.

(b) Forgiveness is that mental attitude by which one overlooks an injury or wrong done to one by another, whether physical, mental or moral. Forgiveness restores broken relationship, especially when it is accompanied by forgetting the injury suffered. In fact, forgiveness is more or less divine (Only God can truly forgive); human beings merely pardon.