Forgive his executioners. That's what Jesus asked of God as he was dying on the cross. "Father, forgive them, for they know not what they do," He said.
With Christ's death and the celebration of his resurrection, today, on Easter, the world's two billion-plus Christians are reminded of a teaching central to their faith - that if God can forgive the worst of sins, so can they.
"The Easter story in our tradition of Christ's movement from victim to victor is a model of how we can respond to tragedy in our own lives, and to move beyond it," said Rev. Chloe Breyer, an Episcopal priest in New York City.
Fine in theory, but hard in practice.
Ask victims of Bernie Madoff's multi-billion dollar Ponzi scheme.
"I want his family to feel the pain they've inflicted on our family," said one man.
Are there wrongs that are unforgivable, such as the Nazi death camps during the Holocaust? Are the families who lost loved ones on 9/11 ready to forgive the hijackers?
Caught up in their anguish, most Americans never even heard about a horrific car accident a few days after the Twin Towers tragedy, or about the drunk driver who killed eight members of the University of Wyoming's cross country team.
Shatto's son Shane was one of the dead runners. "I was proud about his uniform," he said. "To have your son on a university team is a big deal."
Shatto put up a cross with eight names on it at the crash site.
Debbie McLeland also lost her son, Morgan. "He died there on the highway, alone, without me," she said. "I couldn't say 'goodbye.'
"That bothered me for quite a while. And then I thought about it and I thought how afraid he must've been, you know, because you're a mom."
Clint Haskins says he has no memory of that night. A 21-year-old senior at the University of Wyoming on the rodeo team, he'd been drinking for hours at a party, then a bar.
He's now serving a 14- to 20-year sentence for 8 counts of vehicular homicide.
"I just can't live my life that way. I cannot live my life with a grudge and with hate and anger in my heart, I just can't," said McLeland (left).
But Shatto said, "If I forgive him, then my son died for nothing. And I guess that's the part that drives me. I don't want these eight boys to die for nothing."
As his son was, Shatto is a volunteer fireman. He's worked tirelessly against drunk driving. He's on committees, and gives talks.
So does Debbie McLeland. "There is no safe way to drink and drive," she said at one appearance.
"There hasn't been a single day since this happened that I don't realize what I'm responsible for," Haskins said.
The sight of the two of them, embracing, shocked and angered the other parents.
McLeland is unapologetic.
"I'm really angry about a lot of things and I'm really angry that I don't have my child," she said. "But I have to deal with this and I have to deal with it how I can. And I can't deal with it without forgiving."
Clint Haskins is expected to come up for parole in another couple of years and, yes, Debbie McLeland (Morgan's mother) and Kerry Shatto (Shane's father) disagree over whether the person who took their sons' lives should go free.
"I want him to have a life," McLeland said. "You know, my son has no life. I want Clint to have a Life. I want him to have a wife and children and a family."
But Shatto said, "He gets out some day and he gets to have a family, and he gets to see his parents again, but my son will never get any of that. I don't have the forgiveness, that's just not in my heart to do that."
Kerry Shatto and Debbie McLeland: How could they come to opposite conclusions? It seems that human beings are driven by two very different impulses at the same time.
"Revenge and forgiveness are like two sides of the coin," said Michael McCullough, a psychology professor at the University of Miami.
"We know absolutely that revenge is this universal feature of human nature, but we also know now that there is a natural, evolved capacity to forgive that also exists in every human mind on the planet."
We're taught that revenge is like a disease. But in his recent book, "Beyond Revenge: The Evolution of the Forgiveness Instinct" (Josey-Bass), McCullough argues otherwise.
"This is one of the real surprises from neuroscience over the last decade: Revenge is not coming from some sick, demented, ill part of the brain," McCullough said. "The brain system that produces revenge is the same system we use when we're looking for something to eat when we're hungry.
"Desire: it's the desire to satisfy a craving," he said.
Forgiveness involves the part of the brain associated with empathy (the anterior cingulate cortices).
"So forgiveness is born in part of the experience of somebody else's pain," McCullough said. "It doesn't feel very good to people to seek revenge against people they feel sorry for."
When somebody harms us, we get upset emotionally and physically. We might hunger for revenge - but forgiveness is better for our health.
"You want to feel better," McCullough said. "Revenge can do that in the short term, but it's kind of like junk food, really, in terms of happiness. In the long term, what forgiveness does is it restores valuable relationships, and that has a long term, sort of satisfying quality to it."
There's the old saying that forgiveness is divine. "In Christianity, forgiveness is a central tenet," said Rev. Breyer.
Which brings us back to religion. Forgiveness, says Rabbi Simkha Weintraub, is central to Judaism.
At a conversation with representatives of four different faiths arranged by the Interfaith Center of New York, Imam Shamsi Ali said, "The most frequent attribute of God mentioned in the Holy Koran is His mercy and forgiveness."
Lama Pema Wangdak talks about forgiveness as part of a quest toward a perfect, timeless principle of patience: "Part because we have nothing to forgive to anybody, part because we don't see the enemy outside. We see enemy inside of us."
"There have been holy wars in the name of religious faith for centuries," said "Teichner. "How can the same religions that promote forgiveness also condone and take part in war?"
"Those who were involved in the revenge, those were involved in the wars, are people who try to follow religions, but often time they fail," said Imam Shamsi Ali. "Some of those are using Islam as justification for their own purposes. And I think bin Laden in his way is one of those."
But for Imam Shamsi Ali, being forgiving doesn't mean being a doormat: "Forgiveness doesn't mean for us to be oppressed, because we are human beings and we are realistic that we have that right to defend."
"We do not have a religiously-sanctioned wars," said Lama Wangdak.
But in Tibet last year, Buddhist monks rioted during protests against China, demonstrating a classic dilemma:
"If you're peaceful and kind to the person who is not kind and always harmful to you, are you encouraging him or her? So the risk is always there, whether you do it in a peaceful way or the harmful way. Again, we go back to the principle: Just do the right thing."
Rabbi Weintraub offered an example from Passover: "There's a point in the traditional Seder where we turn to God and we say, pour out your wrath against those nations that have come after us, and hand it over to God."
"Vengeance left to God means forgiveness is our responsibility," said Rev. Breyer. "Don't come asking God for forgiveness, don't expect to be reconciled, unless you have been reconciled between the brother or the sister that you have offended.
"In the Lord's Prayer, we say, 'Forgive us our trespasses as we forgive those who trespass against us,'" said Rev. Breyer.
But as Debbie McLeland and Kerry Shatto know only too well, yes, that's fine in theory, but hard in practice.
Easter is all about giving us hope and the will to keep trying …