How is forgiveness related to mercy?
Forgiveness is being good to those who are not good to you. Mercy is refraining from punishing a person who deserves that punishment because of unjust behavior. Both are moral virtues and so hold that in common. When people forgive, they exercise mercy in that as they forgive they do not give an eye-for-an-eye to the one who hurt you. Instead, the forgiver offers a hand up to the person to come and join you as a person of worth. Mercy as part of forgiveness is a specific expression of mercy in that this mercy is occurring in the context of being treated unjustly by another or others.
There are other examples of mercy that do not include forgiveness. For example, legal pardon is a form of mercy in that a judge may reduce a deserved sentence within a court of law. The judge offering legal pardon never is the one who was treated unjustly by the defendant. Forgiveness, as a personal decision, occurs within the human heart, not in a court of law. Thus, forgiveness includes mercy, but mercy can occur in entirely different contexts than forgiveness. Further, forgiveness does not involve only exercising the moral virtue of mercy. Forgiveness also is an expression of love, particularly agape or the kind of love that is challenging and even costly to the forgiver.