Jesus commands us to forgive others, or else God will not forgive us our sins. Every time we pray the “Our Father,” we acknowledge the importance of forgiving others: forgive us our trespasses, as we forgive those who trespass against us.” In other words, Christians should be the last people to hold grudges.
Not forgiving others certainly has its spiritual costs (such as God not forgiving us!), but scientific evidence suggests that it also has physical costs. Lack of forgiveness causes our bodies to be in a state of stress. This stress contributes to cardiovascular problems, leading to high cholesterol, high blood pressure, and thus increased risk of heart attack. Thus it seems that the sin of being unforgiving affects our whole person, soul and body, just as it strongly affects those whom we refuse to forgive. This is yet another good reason to forgive others as we have been forgiven by Christ.