Often I come across statements from members of the clergy, politicians, and ordinary people quoted in the media, linking "forgiveness" with "healing." Forgiveness isn't a concept from mental health treatment. It's a concept from religion, and in particular, from Christianity. A religious concept has utility for religious persons. For those seeking mental health, a better concept is "moving on."
The purpose of forgiveness in the monotheistic religions is to become more godly or pious. As a psychotherapist, my goal is to help people feel and function better. No psychotherapist should suggest to a patient that he or she forgive those who have hurt them, because such a statement implies that the patient adopt the therapist's religious views. In addition, such a statement could be heard as minimizing the patient's trauma and emotions.
"Forgiveness" implies a change in attitude from the victim toward the offender, and is a statement that the victim no longer seeks retribution. "Moving on" simply means that the victim no longer obsesses or dwells on the offense and seeks to live a normal life unencumbered by emotions generated by the trauma. It is possible to move on without "forgiving" the offender. It is even possible to move on while still seeking retribution in the form of criminal justice or civil law, depending on the amount of time and energy required to pursue justice.
Obsessing over past hurts contributes to depression and PTSD symptoms. The obsession may cause the offender to loom large in the victim's mind and this can contribute to feelings of disempowerment. A saying I heard often when I was a substance abuse counselor--from one recovering patient to another--was "You're letting him rent space in your head!" Actually this is a generous interpretation, because the perpetrator isn't paying any rent to live in the victim's head.
"Moving on" means practicing the old adage "Living well is the best revenge." Psychotherapy for trauma can involve many different techniques, but the ultimate goal should be a better life for the victim. This involves empowering the patient and helping him or her put the past in the past. Many different techniques can help traumatized persons accomplish this. They include various forms of cognitive and behavioral therapy, EMDR, insight-oriented therapy to help the person gain self-understanding and supportive therapy to help the person focus on current goals.
If it's important for you to forgive because of your religious beliefs, then by all means do so. But forgiveness is not a requirement for healing and mental health.