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."
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."