There is scientific research that shows harboring resentment, bitterness, and anger, towards others is not only a mental disorder, but can cause physical illness that can affect metabolism, organ function, immune response, and cause disease. There is a cure for this and it’s called forgiveness. My grandmother was a hard person to love. She was harsh and judgmental, and wouldn’t hold back from telling you how she felt. Her children bore the brunt of her emotion and have suffered at her hand. My great grandmother lived to well over 100 years. You would think her descendants would live a good long life; maybe more of them would have if they were able to forgive easily and move on. Thankfully, my dad never let my grandmother get to him and seems pretty healthy. If you are harboring bitterness, work diligently to try and forgive, it could affect your health and may possibly shorten your life.
Then Peter came up and said to him, "Lord, how often will my brother sin against me, and I forgive him? As many as seven times?" Jesus said to him, "I do not say to you seven times, but seventy-seven times. Matthew 18:21-22