I heard somewhere that Jesus Christ suggested that when we pray we say a prayer that includes: "Forgive us our trespasses as we forgive those who trespass against us." The late Mrs. Edwards, who had probably said the Lord's Prayer a time or two, in not forgiving her husband, was asking that her own sins not be forgiven by God. We are His children and He wants us to forgive one another. I have forgiven any and all of those who have trespassed against me during my last year's medical crises, calling them to forgive personally, where possible, and will continue to do so. Those who read this post: please consider that forgiveness is obedience to the God Who loves you.
Also pay heed to Livius's accurate and noteworthy post.