Remembrance of Jesus' passion will heal your soul of resentment, by making it ashamed of itself when it remembers the patience of the Lord. Some people have wearied themselves and suffered for a long time in order to extract forgiveness. By far the best course, however, is to forget the offences, since the Lord says: "Forgive at once and you will be forgiven in generous measure." (cf. Luke 6:37-38)
