It is rare to meet someone who’s lived the words Christ said on Good Friday from the cross: “Forgive them for they know not what they do.”

But such a person is Tina Chéry of Boston.

She has forgiven the man convicted of shooting and killing her 15-year-old firstborn son Louis Brown. She has visited him in prison. She has befriended his mother. She did not argue against the man’s parole.

She says she couldn’t have managed any of this without her Catholic faith.

“To forgive is to set a prisoner free and discover that the prisoner was you,” Chéry said, quoting theologian Lewis D. Smedes at her office Monday. “But forgiveness doesn’t just happen.

“When Louis died, no man knew how to give me the answer. The system didn’t know how to give me the answer. People in the community and the police didn’t know how to give me answers. So I had to figure out, ‘Okay, Lord, what do I do with this pain and suffering? How do I continue to live and be a mother to my living children? How do I find peace again?’”

She looked for answers in the Bible. “To act justly and to love mercy and to walk humbly with your God,” she said, quoting Micah. “Peace I leave with you; my peace I give you. I do not give to you as the world gives,” she said, quoting John 14. “Do not let your hearts be troubled and do not be afraid.”

She went to her parish priest, Vincent Von Euw of St. Ambrose in Dorchester. “I kiss the ground he walks on,” she said of the now-retired cleric. “He guided me — he didn’t preach — with readings and scriptures and a place to be still. He said God is there. ‘Tina,’ he said, ‘you’re keeping him at a distance. Put your hands down and let him in.’ And when he said that I literally could feel myself putting my hands down and letting God in. So I could be a better mother to my living children. So I’d be able to serve God every day.”

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Louis Brown had hoped to become an engineer — and America’s first black president. He studied hard. But he worried, too, about the increasing violence in his neighborhood. He joined a group called “Teens Against Gang Violence.” On his way to the group’s Christmas party, just five days before Christmas, 1993, he was caught in the crossfire of a gang shootout at 3:15 on a Monday afternoon. He died the following day, leaving behind his mother, father, a younger brother and sister.

We all know the more common scenarios after something horrible like this. Families say justice demands “an eye for an eye.” They tell the killer in court, “I want you to suffer like I have.” Life without parole. Solitary confinement. The Supermax penitentiary. The death penalty.

Tina Chéry chose differently. Within a year after Louis was killed, she founded the Louis D. Brown Peace Institute as a place of healing not just for families whose children were killed in Boston’s inner city, but also for families of children who did the killing. When a child is murdered, Chéry says, not one, but two mothers, two fathers, two sets of siblings and grandparents suffer.

Today, the mother of the man who killed Louis works beside Chéry as an institute volunteer, and Tina Chéry has grown into a local legend. She has introduced a peace curriculum into the schools and the neighborhood. Acting as what she calls “a wedding planner for funerals,” she has helped both families of the dead and the accused deal with media, police, courts; find money to buy coffins and pay for a burials; put together programs for church services with stories about the victims: their favorite foods, sports, games, what they’d hoped to grow up to become. Lots of pictures. And reference books for coping with unexpected questions, as when a little sister wonders, “Am I still a sister since my big brother is dead?” Every year, Chéry organizes a “Mothers Day March for Peace” to raise awareness of Boston’s teen homicides and Boston’s imprisoned teen killers. Thousands have walked along with her.

Yet Tina Chéry, for all this heaviness and loss, is hardly a hunched-down, morose woman. Instead, there is calm, energy, and humor about her. There is both grace and resolve and even, when you watch her smile, a certain radiance.

A year ago, on Good Friday at St. Patrick’s Cathedral in New York, the renowned Jesuit James Martin offered reflections on Christ’s last words, including, “Forgive them for they know not what they do.” In “Seven Last Words,” his short book on those reflections, he referred again to the type of “radical forgiveness” Christ showed on the cross and how some of us — the Tina Chérys among us — manage to achieve such radical forgiveness, too. It is very powerful, but very rare. Yet when we see it, we recognize it, he said. We remember it and even yearn for it. For we understand “that this is how God wants us to live,” and that we have seen in such forgiveness a glimpse, in a human being, of the divine.