The first part of the answer is taken directly from an interview I gave for MercatorNet on July 8, 2015.
But isn’t there a Christian bias built into the idea of forgiveness? Does it work in other faith traditions? Is there a bias in that only Christians can practice the moral virtues of justice, patience, and kindness? If not, why then would not forgiveness be open to all people? We all have the capacity to act virtuously. We may not all reach the same depth of practice, but we all can offer goodness to others in a variety of ways.
Forgiveness, in other words, is open to all people in the world if they choose to exercise this particular virtue when hurt by others. Our research includes people of many faith traditions, as well as those with no faith. When those who choose the forgiveness path finish the work, their well-being tends to improve as seen in the research findings.
Further, there are strong examples of person to person forgiving in the Jewish scriptures (see Genesis 37-45 in which Joseph forgives his brothers. The Qu’ran has a similar story in the book entitled Joseph. Confucian philosophy has the idea of “shu” which includes forgiveness. Hindu writings talk of forgiving those with whom you have been at war. Buddhism, although lacking an explicit word “forgiveness,” talks of loving-kindness and compassion and has stories that clearly show a person forgiving.
Yes, the Christian faith and philosophy, especially as developed by Thomas Aquinas, developed a theology of forgiveness centered on charity or agape love. This, one can argue from a philosophical perspective, is the highest form of forgiveness, to love those who do not love you. Yet, it would be a mistake to say that forgiveness now is only a Christian moral virtue. It is a moral virtue open to all.