OF all the extraordinary events in the life of John Paul II, few can compare with the 21 minutes he spent in a white-walled cell in Rome’s Rebibia prison. Just after Christmas, 1983, the pope visited Mehmet Ali Agca, the man who 30 months earlier had shot him in St. Peter’s Square. He presented Agca with a silver rosary, and something else as well: his forgiveness.

It requires a Christ-like forbearance to pardon a would-be assassin, of course. But how many of us are ready to forgive an unfaithful lover, a scheming colleague or even the jerk who cut into the line at Starbucks? Persistent unforgiveness is part of human nature, but it appears to work to the detriment not just of our spiritual well-being but our physical health as well. The subject is one of the hottest fields of research in clinical psychology today, with more than 1, 200 published studies, up from just 58 as recently as 1997. It even has its own foundation—A Campaign for Forgiveness Research—which sponsored a conference last year with papers on topics like “Exploring Gender Differences in Forgiveness.” (The largest number of papers dealt with forgiveness in marital and romantic relationships, which seem to generate an inordinate amount of interpersonal resentment.) Dr. Dean Ornish, America’s all-purpose lifestyle guru, regards forgiveness as the tofu of the soul, a healthful alternative to the red meat of anger and vengeance. “In a way,” Ornish says, “the most selfish thing you can do for yourself is to forgive other people.”

Research suggests that forgiveness works in at least two ways.

One is by reducing the stress of the state of unforgiveness, a potent mixture of bitterness, anger, hostility, hatred, resentment and fear (of being hurt or humiliated again). These have specific physiologic consequences—such as increased blood pressure and hormonal changes—linked to cardiovascular disease, immune suppression and, possibly, impaired neurological function and memory. One study examined 20 individuals in happy relationships, matched with 20 in troubled relationships. The latter had higher baseline levels of cortisol, a hormone associated with impaired immune function—which shot up even further when they were asked to think about their relationships. “It happens down the line, but every time you feel unforgiveness, you are more likely to develop a health problem,” says Everett Worthington, executive director of A Campaign for Forgiveness Research.

The other benefit of forgiveness is more subtle;

it relates to research showing that people with strong social networks—of friends, neighbors and family—tend to be healthier than loners. Someone who nurses grudges and keeps track of every slight is obviously going to shed some relationships over the course of a lifetime. Forgiveness, says Charlotte van Oyen Witvliet, a researcher at Hope College in Holland, Michigan, should be incorporated into one’s personality, a way of life, not merely a response to specific insults.

In fact, forgiveness turns out to be a surprisingly complex process, according to many researchers. Worthington distinguishes what he calls

“decisional forgiveness”—a commitment to reconcile with the perpetrator—

from the more significant “emotional forgiveness,” an internal state of acceptance.

Forgiveness does not require us to forgo justice, or to make up to people we have every right to despise. Anger has its place in the panoply of human emotions, but it shouldn’t become a way of life. “When I talk about forgiveness, I mean letting go, not excusing the other person or reconciling with them or condoning the behavior,” says Ornish. “Just letting go of your own suffering.”

“It’s a process, not a moment,” says Dr. Edward M. Hallowell, a Harvard psychiatrist and the author of “Dare to Forgive.” Forgiveness, he emphasizes, has to be cultivated; it goes against a natural human tendency to seek revenge and the redress of injustice. For that reason, he recommends doing it with help—of friends, a therapist or through prayer. It was from his faith that John Paul drew the strength to forgive Mehmet Agca, setting (as he no doubt intended) an example for the rest of us. The message is the same whether it’s couched in the language of Christian charity, clinical psychology or the wisdom of Confucius, as quoted by Hallowell: “If you devote your life to seeking revenge, first dig two graves.”