The book of Philemon is a power-packed postcard of an epistle all based upon forgiveness.
The key verses for the book are v.17-20, "So if you consider me a partner, welcome him as you would welcome me. If he has done you any wrong or owes you anything, charge it to me. 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 do wish, brother, that I may have some benefit from you in the Lord; refresh my heart in Christ."