In his new book on mentoring, "Guiding Lights: The People Who Lead Us Toward Our Purpose in Life," author Eric Liu interviewed many of the country's best teachers to discover the qualities of true mentorship. The following excerpt tells of Father Greg, a Los Angeles priest who changes the lives of gang members through unconditional love.

Pico Gardens, Aliso Village. Two of the loveliest names to grace the roll of failed twentieth-century public housing experiments. These projects on the city's eastern edge make up the largest zone of subsidized housing west of the Mississippi. Within them, ten thousand Latino and black gangsters, clumped into sixty gangs, live a littered, empty-calorie imitation of life.

For six years, starting in 1986, Father Greg Boyle, SJ, was the pastor at Dolores Mission, in the heart of Pico/Aliso. It wasn't long before he saw how much more he needed to do than help the helpless mothers, or pray for their boys, or bury them. He started an alternative elementary school. Then he created Jobs for a Future, a program to teach these youth how to find and hold a job. Then he created Homeboy Industries, to help the hardest cases get work by running their own nonprofit businesses-first a bakery, then a silk-screening shop, now landscaping and graffiti-removal businesses. After his rotation in the parish ended, Greg returned to the neighborhood to run Homeboy. This would now be his ministry.

The saga of Homeboy Industries is something out of an after-school special. The Jesuit homeboy, the gangland priest: didn't we see that one on cable? Indeed, Greg has gotten a lot of media attention, particularly as he's criticized the LAPD's approach of hammering the gangs. He speaks with the polish of both a clergyman and a minor celebrity. Some of the lines he uses are, well, recycled. I'd read them in his clips. The stories of the founding, of the rescues and acts of salvation, gleam like stones many times held. Yet what made them refreshing still is that they were never meant to be anything more. They are like stories from the Bible. They are a daily record, a matter-of-fact accounting of the volume of flotsamed lives flowing past. They are a reminder of constant inadequacy. The day I met him he told me he had just buried his 114th child. Greg is free of pretense that what he does is visionary or saintly or world-changing. He is a single human, distributing sandbags against the flood; called to imagine that his labors, in the end, will matter.

With his shaved head and goatee, his unfocused drunken eyes, and his stump of a right arm (a birth defect), Hugo Jimenez was a picture of menace. The words he had for Father Greg at the elevator were hostile too. He said, "I know you-you're the one who doesn't help anyone from our neighborhood." It wasn't just cynicism. It was a geopolitical comment that Greg understood well. Hugo was a member of the Marvelosos, a "Mara Villa" gang at war with the "Sorrenos," gangs of the Mexican mafia, whom Greg more often worked with. He was a gang veteran, his compact body filled with scars and screws and rods from the three times he'd been shot (at thirteen, fifteen, and twenty; in the arm, stomach, and femur). Greg was taken aback by Hugo's hostility but quickly recovered. This was a chance to build a bridge to the Mara Villa. That's why he made sure to get Hugo's number, why he called Hugo early the next morning. Hugo came in at nine. He was twenty-five years old. He had never held a job in his life. He was, as he put it, "allergic to work." Greg put him on the payroll that very day, putting him to work in the office- covering the phones, doing small chores and odd jobs.

One month earlier, Hugo's father had died of complications from diabetes. Greg learned that in the course of their initial interview. It shaped his handling of Hugo, as it shapes his handling of so many ex-homies. The young men who pass through Greg's parish may lack motivation and work skills and capital. But what they lack prior to all of that is a primal attachment. Their "lethal absence of hope," as he calls it, comes from the fact that so many have never been loved and have never been able to love in return. "Gangs are bastions of conditional love," he says. "Homeboy is a community of unconditional love."

Hugo was one of the lucky ones; he'd had a father, he loved his father. Greg's work was to sustain that attachment. He told Hugo at every turn, "You are exactly what God had in mind," and waited for Hugo to inhabit that truth. He didn't tell Hugo or anyone else they could be the first Latino president if they applied themselves. He told them, "You are exactly enough." He didn't woof at Hugo with lectures. He said, "You are everything I would want in a son." If Hugo showed up late, Greg wouldn't yell. He would silently wait, until Hugo hurt inside from the forgiveness. If Greg said, "You're doing a good job, son," it made Hugo want to do a better job. When Hugo decided to get custody of his son, Angel, Greg brought the social worker to see Hugo's closets lined with baby clothes the next size up, ready to be grown into. Greg paid the three hundred dollars to file papers and accompanied Hugo to court. Hugo didn't understand what the judge was saying until he heard, "Full and sole custody to petitioner," and then the hair on the back of his neck stood on end and he looked at Greg and he wanted to cry.

At first, watching and listening to Greg, I was inclined to put some of his actions in a box called "strategic" and others in a box called "sincere." Then, gradually, the boxes became indistinguishable; or, at least, the distinction became irrelevant. Greg tells these lost sons, one after another, that they are in fact exactly enough, that they are everything he would want in a son. And he opens up something primordial in them, something that leads, almost on cue, to huge sobbing and release. The words he spoke to Hugo, the salve of unconditional love that he applied, he has applied to many others as well, often using the very same language. He knew too that Hugo's loyalty would help him broaden his reach to new gangs. What I realized after a while was: So what? So what if he wanted to reach more people? That is his job. So what if his love was produced and dispensed in large batches? Each dose felt real, and each one healed.

Hugo proved to be a diligent worker. Over the next two years he started taking on more responsibilities, using computers for data entry and record keeping, becoming more vital to the operation. The next challenge for him, Greg said, will be to assert his value in the world beyond Homeboy Industries. Every Saturday morning Hugo goes to the cemetery to visit his father. He said to Greg once, "I wish I could show him what I'm becoming. I wish I could see his face, because all I gave him when he was alive was grief." Greg answered, "He is seeing you now." And that was enough for Hugo. It was enough to keep him going that day, to get him out of bed the next morning and the morning after that, to help him take care of himself and his boy. It was enough to make Hugo resolve, silently, that he wanted to be for Angel the kind of father Greg had become for him.

The day after they met in the street, Johnny showed up at Greg's office. Greg got him a job as a gardener for a pastor in Santa Monica. Greg knew better than to expect linear progress from there, but even by the chaotic standards of this subculture, Johnny's next phase of life would be an utter mess. He did the gardening for a while, then got arrested on a gun charge and spent six months in jail....He went to prison for sixteen more months. When he got out this time, there was a message from Greg to come see him. He joined the Homeboy graffiti cleanup crew, which does contract work for the city, and started working again. That ended when Greg got a call that Johnny had been gangbanging and partying using the crew truck. Johnny had no memory of it.

At the root of it all was addiction. G, or G-Dog, as Johnny and others came to call Greg, had called it. You've got to get past the drugs, he told Johnny in their first meeting. During his first three years on the crew he was still smoking pot and snorting cocaine and drinking all hours. "G would see I was losing weight from all the coke and he would ask about it and I would lie. And he would say, `I'll take your word for it.' But he knew I was lying."After the work truck incident, Johnny agreed to go to an outpatient rehab program. He stayed clean for a month before he figured out how to cheat the system.

When he got kicked out of rehab, G gave him an ultimatum: check into an inpatient program, or sever ties with Homeboy. Johnny thought about it, and "out of respect for G," granted himself one last run. He got a motel room during a long weekend and there he filled his lungs and veins with every substance he could abuse. Tuesday morning he came to work and told G he was ready. He checked into Warm Springs for ninety days and, as of the day we met, he'd been sober for a hundred and thirty-two. Today he is back on the graffiti crew, as one of the supervisors.

I asked Greg what it was he'd seen in Johnny that justified his faith in him. Greg said, "It wasn't what I saw in Johnny; it was being a parish priest. You have to try to imitate the God you believe in. Why should I deal in a language of bitterness and disappointment?" He gave Johnny "little marks to hit." When he hit them, it was progress. When he didn't hit them, it was progress. The attitude was to declare victory at all times, even when two steps forward meant eight steps back. This was core to Father Greg's MO. He was not naïve, or blind, or a weak-willed enabler.

"No hanging, no slanging, no banging" is the only clearly stated requirement for entry at Homeboy. Yet Greg could see that the troublemaking and the drug abuse and the graffiti and gunplay all continued. He simply refused to use it as an excuse. He refused to reinforce the message of failure that had shaped these boys all their impoverished lives. Their parents and siblings are addicts. Their schools are disasters. Their homes are shabby. Their gangs, ultimately, are unreliable refuges. Shame and disgrace, and shame and disgrace over the shame and disgrace, are all they have known. Greg didn't lay on the guilt. He gave Johnny a choice: you can leave this way of life, or not.

The idea of agency is powerful, but best taught in subtle, indirect ways. I never heard, or heard of, Greg delivering a sermon to these boys or even an overtly religious message about personal responsibility and personal agency. What I heard about was his birthday calendar. On his cluttered desk is a worn notebook that reminds him every day to pick up the phone and call Felipe or Jaime or Armando, homies who've already passed through his program, and say, "Happy Birthday, son. I am glad you were born."

Sometimes he can't get to the call till after eleven P.M., at the end of a long day, but he will place it before the night is over. It's often the only call these young men will get. For many, it's the first time their birthday has ever been properly acknowledged. The two-minute call is something that makes them feel firme, proper, like they can hold their head up high. It's the feeling they get when they do their homework well for the first time and burst into Greg's office to tell him. The feeling they get after their first day on the job.

Johnny Ortega has a routine now. He gets up every day at five, while Greg and the city still sleep. He and his four-man crew, ex-homies from rival gangs, will cruise through Boyle Heights and try to take down last night's tags before the sun is up. He has three or four pages of "hot spots" they have to hit. It'll take them till early afternoon. He drives and scans the city. He searches the blocks, the walls and corners, for the telltale signs of this gang or that. He reads the coded language of assertion and aggression and insult painted on every surface. Sometimes, he will remember what it was like to belong, to color these walls and not erase them. Primera Flats was his gang. Sometimes, naturally, the memory of demons now dormant will clutch his innards. But the pangs eventually pass. He will remind himself, "I don't want to die over a neighborhood." He will think of Father Greg and remember, "I don't want to let G down."

When Johnny first came to G he was a teenager. Now he is thirty-four, with lines in his face and three children in his home. He is, for now at least, sober and clean. His children know the difference. "They're happy to see me now." What time he lost, what time he has left-these don't matter. He is present today. Three years ago, before Hugo came to Homeboy, he would never have spoken to me, let alone told of his father and his hopes and fears. He could never have imagined working all week and earning a paycheck and buying a Happy Meal for a homeless man at the on-ramp, as he did the other day. He knows God brought him and Greg together in that elevator. God did it for a reason. He does everything for a reason.

When Greg was diagnosed with leukemia, the news seemed to rock everyone around him but not him. "People here have been able to ask me, `How are you feeling?' " he marvels. "And that is remarkable for people whose own burdens are more than they can possibly bear." As he began chemo, Johnny and Hugo and a thousand other souls walked in and all asked the same question: What do I have that you need? Organs? Blood? Anything- tell me. They did the very thing he had done for them: they came to the hospital....

For Greg, the experience has been "like being awake at your own funeral, or sitting up in your coffin," he says, smiling. "It has been a graced experience." He recalls the old Ignatian monks whose mantra was Today. He finds God in all things now-a multicolored leaf, a Flannery O'Connor story, a group of fellow chemo patients. Chemo itself was "interesting" more than frightening. He understands more deeply now that the opposite of love is not hate but fear, and that he cannot live in fear.

"I used to think my job was to save," Greg says. "Now I don't think I can save anyone. The focus ought to be on how to stay faithful to an approach you believe in and to your principles. Anyone can do this work if you have a pulse and your head together." He tells me a story about a kid he'd once helped, whose brother had just killed himself. The kid had a dream: He was with Greg in a dark and silent room. He knew Greg was there. He knew Greg had a flashlight. Greg turned it on, and aimed the beam at the light switch. And the kid thought to himself, I'm the only one who can flip the switch. This child's dream has been on Father Greg's mind a lot. "It's freed me from wanting to turn the light switches on for people. I feel content to have a flashlight and to know where to aim it. Because then, it's who saved whom? Hugo saved himself when he came in to work at nine." He draws a breath. "To say nothing of God's role."