Unforgiveness is classified in medical books as a disease. According to Dr. Steven Standiford, chief of surgery at the Cancer Treatment Centers of America, refusing to forgive makes people sick and keeps them that way.
With that in mind, forgiveness therapy is now being used to help treat diseases, such as cancer.
"It's important to treat emotional wounds or disorders because they really can hinder someone's reactions to the treatments, even someone's willingness to pursue treatment," Standiford explained.
Of all cancer patients, 61 percent have forgiveness issues, and of those, more than half are severe, according to research by Dr. Michael Barry, a pastor and the author of the book, The Forgiveness Project.
"Harboring these negative emotions, this anger and hatred, creates a state of chronic anxiety," he said.
"Chronic anxiety very predictably produces excess adrenaline and cortisol, which deplete the production of natural killer cells, which is your body's foot soldier in the fight against cancer," he explained.
Barry saif the first step in learning to forgive is to realize how much we have been forgiven by God.
"When a person forgives from the heart – which is the gold standard we see in Matthew 18, forgiveness from the heart – we find that they are able to find a sense of peacefulness. Quite often our patients refer to that as a feeling of lightness," he said.
Barry said most people don't realize what a burden anger and hatred were until they let them go.