To forgive the truly horrible is to kiss the robe of God, to emulate no less a figure than the dying Jesus Christ. Father, forgive them; for they know not what they do. Those words leapt into Colleen Kelly’s mind when she realized her brother was gone forever, buried in the smoldering graveyard that had once been the World Trade Center. The architectural pride of Wall Street, an icon of America’s power and beauty, was now a symbol of incomprehensible horror, an unlikely resting place for Bill.

Bill was in financial services, a salesman for Bloomberg L.P. He did not normally work at the World Trade Center. So the family initially had no idea he was there. But once the planes plowed into the towers, New Yorkers everywhere picked up phones, mostly to reassure one another life would go on.

Colleen learned that Bill had been attending a conference at Windows on the World, the restaurant on the 107th floor of the World Trade Center. And that September day it fell on her, a nurse and mother of three living in the Bronx, to make the trek into Manhattan. Sustained by the hope, the dream, that Bill had somehow made it out, she wandered from hospital to hospital, inquiring about her brother. Eventually she grew cognizant of an ominous fact: though doctors and nurses abounded, there was no one for them to treat — no one, at any rate, from the World Trade Center. "That’s when I knew Bill was dead." And that’s when the words of Jesus Christ flashed through her mind. Father, forgive them; for they know not what they do.

She realized the words made absolutely no sense, not in the present context. The terrorists had clearly known, with horrifying precision, exactly what it was that they were doing. Her response, she later concluded, stemmed not from an urge to forgive but from an almost instinctive resolve not to hate. The leap to Jesus’ words on the cross was her mind’s way of reaffirming values that she had clung to all her life, values that embraced peace over war. In the face of the most wrenching provocation imaginable, she rejected vengeance. "These terrorists had taken my brother," she told me over lunch many months later, "and I wasn’t going to let them take anything else."

Colleen was among the founders of September Eleventh Families for Peaceful Tomorrows. The families sought to honor their lost loved ones by condemning vengeance and violence — even if that meant visiting Iraq as America prepared to make war on Saddam Hussein, or meeting with the mother of Zacarias Moussaoui (the so-called twentieth hijacker) in an effort at dialogue and reconciliation.

It is not my purpose here to consider the political effectiveness or appropriateness of such efforts. I am more interested in Kelly’s initial impulse, in the notion that forgiveness, albeit as a proxy for a larger set of values, could even be considered in the context of acts so vile as those perpetrated by the September 11 terrorists.

Are some things so awful they cannot be forgiven? Or does wisdom lie closer to Kelly’s instinctive response? Are some acts so horrifying, so incomprehensible, so beyond the scope of normal humanity, that they must be forgiven — or at least consigned to that section of the heart most open to mercy and compassion, most inclined to let go of the urge to revenge?

A developing school of psychology argues that forgiveness is a gift not only to the person forgiven but to those who grant the gift, those strong enough to forgive. Robert Enright, a leader in that school, sees forgiveness as a route to personal freedom, a way of rejecting the self-imposed, self-reinforcing label of victim and escaping an ultimately soul-destroying maze of anger and resentment. Indeed, practicing forgiveness may even lower your blood pressure, while relieving other ailments — physical and mental — traceable to the stress of chronic anger.

It is not just a handful of psychologists, but also holy men and philosophers, who trumpet the benefits of a forgiving soul, who see forgiveness as much of the answer to what is wrong with mankind. Like all true believers, they overreach; many would turn the whole world into the church of forgiveness. And they tend to seek converts where they cannot (and perhaps should not) be found. But I believe they are onto something important — at least for those capable of or willing to take on the challenge of living the attitude these particular believers promote.

In Forgiveness Is a Choice Enright tries to explain what forgiveness is and what it is not. It is not giving up the ability to hold people accountable or letting wrongdoers off the hook. It does not mean forgetting the wrong that they did, or becoming complicit in continued abuse. It does not mean turning your head as a pedophile abuses children or a violent husband batters his wife. Instead — and he borrows the definition from philosopher Joanna North — forgiveness means responding to unjust hurt with compassion, with benevolence, perhaps even with love. While it does not deny the right to resentment, it does not wallow in bitterness; nor does it necessarily demand that the perpetrator respond with gratitude or grace. Or as Enright and Richard Fitzgibbons spell it out in Helping Clients Forgive, "People, upon rationally determining that they have been unfairly treated, forgive when they willfully abandon resentment and related responses (to which they have a right), and endeavor to respond to the wrongdoer based on the moral principle of beneficence, which may include compassion, unconditional worth, generosity, and moral love (to which the wrongdoer, by nature of the harmful acts, has no right)." Michael McCullough, another psychologist and forgiveness researcher, defines the concept considerably less grandly — as ending estrangement and letting go of resentments and of the urge to revenge.

Granting the kind of forgiveness Enright endorses seems a tall order for a mere mortal — even one who hopes it will lower her blood pressure and otherwise make her a better, more healthy human specimen. Yet I have repeatedly found myself amazed at the capacity of and willingness of otherwise ordinary human beings to return injury with compassion.

Consider Azim Khamisa, an elegant, international investment financial consultant who is of Persian and Indian lineage. Khamisa was born in Kenya, educated in England, and immigrated to the United States in 1974. He was living in La Jolla, California, in January 1995 when tragedy shattered his theretofore peaceful existence.

After returning from a business trip to Mexico City, Khamisa had gone directly to a party. Having just endured a painful breakup with his then-girlfriend, Khamisa was soaking in the warmth and goodwill from a group of people particularly close to him. Khamisa and his friends left the party together and went to his home. Once they departed, an exhausted Khamisa collapsed in bed; he apparently slept through the knocks on the door later that night. The next morning, Sunday, his maid brought him a business card from a policeman — a homicide detective — that had been left in his door.

Khamisa called. It was then that he received the heart-stopping news that Tariq, his son, was dead. At first, Khamisa refused to believe it. The news was so shocking, so unexpected that he simply couldn’t accept it. He hung up, dialed Tariq’s number, and waited with every expectation that his son would come on the line. Instead, Tariq’s fiancée answered, sobbing.

At that moment, the truth sank in. It was as if a nuclear bomb had exploded inside, tearing him into a million pieces, recalled Khamisa. "Life drained out of me." His soul left his body, ascending to another plane. "I felt the long arms of my Maker."

In time, Khamisa’s soul returned, and he had no choice but to face facts. Tariq, then twenty and a student at San Diego State University, had been at his pizza delivery job that Saturday night when a woman ordered a pizza. Her call aroused no particular suspicions, nor did the delivery address — a building in a lower-middle-class community not far from the university. When Tariq arrived, however, he found that the given apartment number did not exist.

Four gang members lay in wait. They pounced as Tariq headed back to the car. He made it inside, but the eighteen-year-old gang leader was not about to let him go. "Bust him," he ordered a fourteen-year-old soldier. The bullet passed through the window, through Tariq’s shoulder, underneath one arm and came out under the other. The youths fled. A priest in a nearby building heard the shot and rushed out of the shower and into the street. He tried CPR, but Tariq, his aorta ruptured, was already dead.

One of Khamisa’s close friends had also lost a son to murder. In an effort to comfort the grief-stricken Khamisa, the friend expressed the hope that Tariq’s killers would "fry in hell." He also talked about his own lost son, and about how, if he could only get his hands on the murderer, he would execute not just the killer but "his whole clan." To Khamisa, who harbored no lust for revenge, the confession brought no relief.

He buried his son that Thursday. "My rage came on Friday," Khamisa recalled. "I was angry, but not at Tony [the shooter]," he told me. His anger singled out no particular individual; it was something more generalized, aimed at whatever it was in American society that had produced a fourteen-year-old kid who had killed a stranger on command. "My rage was mostly directed at society and my country." For the eighth-grade murderer, he felt compassion.

Khamisa’s religious beliefs played a role in his reaction. A Shiite Muslim, Khamisa belongs to the Ismaili sect and extols Sufism — an "inner, mystical, or psycho-spiritual dimension of Islam," in the words of Alan Godlas, a scholar at the University of Georgia. Khamisa’s faith is "more eastern, more Buddhist than fundamentalist." It is about a quest for "the hidden meaning in the faith," Khamisa explained.

That faith, as Khamisa practices it, embraces peace, forgiveness, love; and it doesn’t allow much time for mourning or for self-pity. "We mourn the first…