"At a time when our discourse has become so sharply polarized," President Obama told the "Together We Thrive: Tucson and America" memorial service at the University of Arizona's McKale Memorial Center, "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."
Among the injured when a gunman opened fire at a "Congress on Your Corner" event for Rep. Gabrielle Giffords, D-Ariz., outside a supermarket Saturday morning in Tucson was Giffords herself. The congresswoman was shot a point blank range in the back of the head and has been in critical condition ever since.
Obama revealed during his speech that after he visited with her at the hospital earlier in the day, Giffords opened her eyes for the first time.
"Gabby opened her eyes, so I can tell you: She knows we are here, she knows we love her and she knows we are rooting for her throughout what will be a difficult journey," Obama told the cheering crowd.
House Minority Leader Nancy Pelosi, D-Calif., Sen. Kirsten Gillibrand, D-N.Y., and Rep. Debbie Wasserman Schultz, D-Fla., were in the room when Giffords opened her eyes, a congressional source told ABC News.
Giffords had her eyes open for about a minute total and was able to raise her whole arm, Gillibrand told ABC News, adding that everyone in the room was crying. Afterwards, Gillibrand said, the doctor declared it to be a major step forward for the patient.
"We had been telling her that she was inspiring the country with her courage and that we couldn't wait to take her out to pizza and a weekend away," Gillibrand said through a spokeswoman. "Then, after she heard our voices and the encouragement of Mark and her parents, she struggled briefly and opened her eyes for the very first time. It was a miracle to witness."
"My heart was overflowing with love for my friend Gabby today," Wasserman Schultz said in a prepared statement. "It was absolutely incredible to witness Gabby open her eyes. I am confident that the power of love, friendship and the prayers of a nation will help bring Gabby back to her family, her friends and her beloved constituents."
Standing O for 'O'
The president and first lady were greeted at the Tucson memorial by a standing ovation as they walked into the packed stadium.
"I have come here tonight as an American who, like all Americans, kneels to pray with you today, and will stand by you tomorrow," the president told the crowd.
You can read the president's full remarks HERE and click here for full ABC News coverage of the tragedy in Tucson.
As he listened to the ceremony before speaking, Obama was visibly emotional. Gifford's husband, space shuttle Capt. Mark Kelly, sat between the first lady and Secretary of Homeland Security Janet Napolitano.
Obama opened by quoting Psalm 46, saying, "There is a river whose streams make glad the city of God, the holy place where the Most High dwells. God is within her, she will not fall; God will help her at break of day."
The president focused on the victims and encouraged Americans to live up to the expectations of one of them, 9-year-old Christina Taylor Green.
"I believe that for all our imperfections, we are full of decency and goodness, and that the forces that divide us are not as strong as those that unite us," he said. "That's what I believe, in part because that's what a child like Christina Taylor Green believed.
"Imagine: Here was a young girl who was just becoming aware of our democracy; just beginning to understand the obligations of citizenship; just starting to glimpse the fact that someday she too might play a part in shaping her nation's future," the president said. "She saw all this through the eyes of a child, undimmed by the cynicism or vitriol that we adults all too often just take for granted."
Obama: Victims 'Represented What Is Best in America'
One-by-one, Obama honored each of the six people killed, who, he said, "represented what is best in America."
Besides Christina, those killed were Judge John Roll, Dorothy Morris, Phyllis Schneck, Dorwan Stoddard and Gabe Zimmerman, the only of Giffords' staff members to perish in the shooting.
The president also praised "those who saved others" -- the nurses, doctors, policemen, staffers and bystanders who put themselves in harm's way to try and stop the shooter.
"They remind us that heroism does not require special training or physical strength. Heroism is here, all around us, in the hearts of so many of our fellow citizens, just waiting to be summoned -- as it was on Saturday morning," the president said.
Striking a tone similar to President John F. Kennedy in his 1961 inauguration speech, Obama called upon the nation to respond with charity towards one another.
"We cannot and will not be passive in the face of such violence. We should be willing to challenge old assumptions in order to lessen the prospects of violence in the future," he said. "But what we can't do is use this tragedy as one more occasion to turn on one another.
"As we discuss these issues, let each of us do so with a good dose of humility," he added. "Rather than pointing fingers or assigning blame, let us use this occasion to expand our moral imaginations, to listen to each other more carefully, to sharpen our instincts for empathy and remind ourselves of all the ways our hopes and dreams are bound together."
In perhaps the only mildly political moment of the speech, the president referenced a "discourse [that] 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."
The president asked, "Rather than pointing fingers or assigning blame, let us use this occasion to expand our moral imaginations, to listen to each other more carefully, to sharpen our instincts for empathy and remind ourselves of all the ways our hopes and dreams are bound together. ... Let's make sure it's not on the usual plane of politics and point scoring and pettiness that drifts away with the next news cycle."
The president ended his speech where he began, honoring a victim: Christina Taylor Green, he said was, "so deserving of our good example ... I want us to live up to her expectations. I want our democracy to be as good as she imagined it. All of us -- we should do everything we can to make sure this country lives up to our children's expectations."
Green was born on Sept. 11, 2001, one of 50 babies born that day featured in the book "Faces of Hope." The president highlighted that within the book, on either side of Green's photo, were the words, "I hope you help those in need. I hope you know all of the words to the National Anthem and sing it with your hand over your heart. I hope you jump in rain puddles."
The president concluded: "If there are rain puddles in heaven, Christina is jumping in them today. And here on Earth, we place our hands over our hearts, and commit ourselves as Americans to forging a country that is forever worthy of her gentle, happy spirit."
Polishing the Tucson Memorial Speech and DC Call for Reflection
The president worked throughout last night on the speech, sources said, and was editing his text on Air Force One flying from Washington to Tucson this afternoon.
The speech itself, just under 20 minutes, was a part of a broader, hour-long program. The somber event included music, moments of silence, prayers and other speeches.
During times of national tragedy the president is called upon, formally and informally, to serve as a compass for the nation going forward, sorting though grief and bringing healing and hope in the face of tragedy.
Shortly after touching down in Arizona, the president and first lady headed to University Medical Center in Tucson to visit Giffords and her husband, Kelly, as well as other victims of Saturday's shooting.
The first couple also was joined Attorney General Eric Holder, Napolitano, and Sens. John McCain, R-Ariz., Jon Kyl, R-Ariz., and John Barrasso, R-Wy.
Dr. Peter Rhee led the bipartisan delegation around the hospital, visiting the wounded first and then with the families of the deceased.
"The president wanted to begin this solemn trip by stopping first at the hospital where Congresswoman Giffords and others continue to recuperate," White House Press Secretary Robert Gibbs said.
The president and first lady arrived against the backdrop of an historic and sober day in the nation's capitol. Earlier today, the House passed a resolution paying tribute to their gravely injured colleague.
A tearful speaker of the House, Rep. John Boehner, R-Ohio, opened House proceedings today with a call to reflection: "We are called here to mourn an unspeakable act of violence," Boehner said.
"Look at Tucson right now and you will be reminded that America's most plentiful source of strength is her people," he continued. "No act, no matter how heinous, will stop us from doing our duty and being among the people we serve."
Giffords' office issued a statement in response: "The outpouring of support from the people of Arizona and Americans across the country has been truly moving. We appreciate everyone's thoughts and prayers during this difficult time. The resolution before the House today was a further reflection of the best of America -- one after another, members came to the floor, without party labels, in support of those impacted by this tragedy. They honored the fallen, those recovering, and the heroes who responded quickly to save lives. ... Even during the darkest times, our nation's capacity for kindness and fellowship reminds us of the best in people. To everyone who has expressed well wishes, we offer our most heartfelt thanks."
The outpouring of support in Tucson tonight was evident as thousands waited in line, some sleeping on the ground overnight, to enter the McKale Memorial Center this afternoon. The university set up an area to handle the overflow of students and other attendees who camped out on the sidewalk under the desert sun.
The Program: 'Together We Thrive: Tucson and America'
The hour-long memorial this evening was thrown together quickly as a way to gather and mourn. A Native American blessing opened the program followed by a welcome speech from University of Arizona President Robert N. Shelton and, of course, the playing of the National Anthem.
Arizona Gov. Jan Brewer and two student speakers from the university, student body president Emily Fritze and David Hernandez, also made remarks.
Napolitano, who formerly was Arizona's governor, and Attorney General Eric Holder both spoke. Napolitano quoted from the book of Isaiah, and Holder read from the second letter of Paul to the Corinthians.
Supreme Court Justice Anthony Kennedy represented the judicial branch in the audience, and House Minority Leader Nancy Pelosi, D-Calif., Reps. Paul Gosar, Jeff Flake, Trent Franks, Ben Quayle and Dave Schweikert represented the legislative.
The memorial service concluded with the signing of the hymn "Come Thou Fount."
What Tucson Wanted to Hear
The feeling in Tucson was a bit divided about what the president would and should say. All agreed the president's message should be one of unity and healing focused on the victims of the tragedy.
"I believe that the president should maybe focus more on the families and the healing aspect of what happened -- the tragedy," said Lisa Engelberg, a 30-year resident of Tucson.
Engelberg added that as the community heals, there should not be politics in the president's message tonight.
"I think today might need to be about those who were the victims of the shootings and their families and not so much the politics," she said.
Seth Landy, a resident of Tucson, said the community just needed some "guiding words" -- but confessed that at some point politics is going to have to be part of the discussion.
"I do think it's important that the president talk about the victims and the families, you know, but eventually the politics are going to have to come into it," Landy said. "I think that gun control needs to come up tonight, I really do, you know, because so many people are talking about this."
Rishelle Baines, a student at the University of Arizona, said the politics of the shooting is a part of the president's message -- but it shouldn't be the emphasis.
"I just think we have to step aside and really just worry about everybody healing and coming together," Baines said. "Yes, politics is a part of it but I really think first we just have to be human and think about everybody healing. ... That's the biggest thing."
Mark Speers of Tucson, among the many who waited in line for the speech, said Obama's appearance tonight was -- in essence -- almost like the moment of silence he observed on the South Lawn at the White House on Thursday.
"It wasn't about him saying anything at that moment," Speers said. "I really feel that he would do just that. It's about the cause of what just happened and reaching out to people to kind of heal some of that."
The politics of the tragedy will be more appropriate to discuss on another day, Speers said.
"A heated debate seems to already be going on," Speers said, "so I think it's important that today happens for what it is, and I think tomorrow is another day to present that."
ABC News' Dan Harris and Michael S. James contributed to this report.