TUCSON, Ariz. — Summoning the soul of a nation, President Barack Obama on Wednesday implored Americans to honor those slain and injured in the Arizona shootings by becoming better people, telling a polarized citizenry that it is time to talk with each other "in a way that heals, not in a way that wounds." Following a hospital bedside visit with Rep. Gabrielle Giffords, the target of the assassination, he said: "She knows we’re here, and she knows we love her."

In an electrifying moment, the president revealed that Giffords, who on Saturday was shot point-blank in the head, had opened her eyes for the first time shortly after his hospital visit. First lady Michelle Obama held hands with Giffords’ husband, Mark Kelly, as the news brought soaring cheers from thousands gathered for a memorial service.

Obama bluntly conceded that there is no way to know what triggered the shooting rampage that left six people dead, 13 others wounded and the nation shaken. He tried instead to leave indelible memories of the people who were gunned down, and to rally the country to use the moment as a reflection on the nation’s behavior and compassion.

"I believe we can be better," Obama said to a capacity crowd in the university’s basketball arena and to countless others watching around the country.

"Those who died here, those who saved lives here — they help me believe," the president said. "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."

In crafting his comments, Obama clearly sought a turning point in the raw debate that has defined national politics. He faced the expectations to do more than console, but to encourage a new day of civility, all without getting overly political in a memorial service.

Obama settled on a theme of challenging the country to have a debate that is worthy of those who died. He tapped into the raging debate about the role of incendiary rhetoric without dwelling on it. "Let’s remember that it is not because a simple lack of civility caused this tragedy. It did not," the president said.

After offering personal accounts of every person who died, he challenged anyone listening to think of how to honor their memories, and he was not shy about offering direction. He admonished against any instinct to point blame or to drift into political pettiness or to latch onto simple explanations that may have no merit.

The president said it was OK, even essential, for the country to suddenly be debating gun control, mental health services and the motivations of the killer.

But then he added: "At a time when our discourse has become so sharply polarized — at a time when we are far too eager to lay the blame for all that ails the world at the feet of those who think differently than we do — it’s important for us to pause for a moment and make sure that we are talking with each other in a way that heals, not a way that wounds," the president said.

The shooting happened as Giffords, a three-term Democrat who represents southern Arizona, was holding a community outreach event in a Tucson shopping center parking lot Saturday. A gunman shot her in the head and worked his way down the line of people waiting to talk with her, law enforcement officials said. The attack ended when bystanders tackled the man, Jared Lee Loughner, 22, who is in custody.

Obama’s speech, by turns somber and hopeful, at times took on the tone of an exuberant pep rally as he heralded the men who wrestled the gunman to the ground, the woman who grabbed the shooter’s ammunition, the doctors and nurses who treated the injured, the intern who rushed to Giffords’ aid. The crowd erupted in multiple standing ovations as each was singled out for praise.

The president ended up speaking for more than half an hour, doubling the expected length of his comments.

Memories of the six people killed dominated much of Obama’s speech.

The president, for example, recalled how federal Judge John Roll was on his way from attending Mass when he stopped to say hello to Giffords and was gunned down; Dorothy Morris, shielded by her husband, but killed nonetheless; and Phyllis Schneck, a Republican who took a shine to Giffords, a Democrat, and wanted to know her better.

He spoke at length of 9-year-old Christina Taylor Green, the only girl on her Little League team, who often said she wanted to be the first woman to play in the major leagues. She had just been elected to the student council at her elementary school and had an emerging interest in public service.

"I want us to live up to her expectations. I want our democracy to be as good as she imagined it," Obama said. The little girl was born on Sept. 11, 2001, and had been featured in a book about 50 babies born that day. The inscriptions near her photo spoke of wishes for a happy child’s life, including splashing in puddles.

Said Obama: "If there are rain puddles in heaven, Christina is jumping in them today."

Obama hit an emotional high point when he told of Giffords opening her eyes for the first time not long after his visit to her bedside.

"Gabby opened her eyes, so I can tell you: She knows we are here, she knows we love her, and she knows that we are rooting for her through what is undoubtedly going to be a difficult journey," Obama said.

The lawmakers who were in Giffords’ hospital room when she opened her eyes were three of her close female friends in Congress: House Democratic leader Nancy Pelosi of California, Rep. Debbie Wasserman Schultz, D-Fla., and Sen. Kirsten Gillibrand, D-N.Y.

"It felt like we were watching a miracle," Wasserman Schultz told reporters traveling back to Washington with her on Air Force One. "The strength that you could see flowing out of her, it was like she was trying to will her eyes open."

Giffords is expected to survive, although her condition and the extent of her recovery remain in doubt.

As finger-pointing emerged in Washington and beyond over whether harsh political rhetoric played a role in creating motivation for the attack, Obama sought to calm the rhetoric.

"Bad things happen," he said, "and we must guard against simple explanations in the aftermath."

He spoke of decency and goodness, declaring: "The forces that divide us are not as strong as those that unite us."

Obama’s appeal for civility played out against a deepening political debate. Earlier in the day, Republican Sarah Palin, criticized by some for marking Giffords’ district with the crosshairs of a gun sight during last fall’s campaign, had taken to Facebook to accuse pundits and journalists of using the attack to incite hatred and violence.

Obama spoke to a crowd of more than 13,000 in the arena and thousands more listened on from an overflow area in the football stadium. About a mile away, at University Medical Center, Giffords lay fighting for her life. Other victims also remained there hospitalized.

The memorial service was an important part of the mourning process for some of those who had lined up hours in advance to gain a seat.

"If we don’t say goodbye and have a chance to say goodbye in an appropriate way, it will linger," said Patty Sirls, 62. "So, for me, it’s a closure."

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Gillian Flaccus in Tucson and Nancy Benac, Erica Werner and Jim Kuhnhenn in Washington contributed to this report. Feller reported from Washington.