"We, the people, declare today that the most evident of truths -- that all of us are created equal -- is the star that guides us still," Obama said in his second inaugural address. "It is now our generation's task to carry on what those pioneers began."
After some bruising fiscal fights in recent weeks, Obama said Americans "are made for this moment, and we will seize it -- so long as we seize it together."
While history says the truths of life, liberty and the pursuit of happiness "may be self-evident, they have never been self-executing; that while freedom is a gift from God, it must be secured by his people here on Earth."
This generation has been tested by crises that have steeled its resolve, the president said.
"America's possibilities are limitless, for we possess all the qualities that this world without boundaries demands," he said.
While he did not address the specific policy issues, Obama did call for action, saying that the nation "cannot afford delay."
"We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat-name-calling as reasoned debate," Obama said outside the U.S. Capitol.
"We must act, knowing that our work will be imperfect," Obama said. "We must act, knowing that today's victories will be only partial, and that it will be up to those who stand here in four years, and 40 years, and 400 years hence to advance the timeless spirit once conferred to us in a spare Philadelphia hall."
He reminded his audience that the oath he took "like the one recited by others who serve in this Capitol, was an oath to God and country, not party or faction -- and we must faithfully execute that pledge during the duration of our service."
The ceremonial swearing-in ceremony -- Obama was officially sworn in Sunday as prescribed by the Constitution -- was under bright sunny skies with temperatures in the 30s.
As Obama made his way to West Side of the Capitol, he shook hands with those in the hallway, pausing to tell House Democratic Leader Nancy Pelosi, "I miss this place." Obama represented Illinois in the U.S. Senate.
U.S. Supreme Court Chief Justice John Roberts administered the oath of office to Obama Monday, as he did in the private ceremony Sunday.
"Congratulations, Mr. President," Roberts said afterward.
"Congratulations," she said after administering the oath.
"Good job," Obama told Biden.
Sen. Charles Schumer, D-N.Y., chairman of the joint inauguration committee, welcomed everyone within earshot to the "celebration of our great democracy."
Schumer also thanked the armed forces "for your bravery, your honor your sacrifice."
To those who doubt whether America can survive its differences and events, Schumer said, "remember America always has been and still are a practical, optimistic and problem-solving people."
"America always rises to the occasion," he said. "America prevails and America prospers."
"It is a good moment to rejoice today," Schumer concluded, "and it is the perfect moment to renew our collective faith in the future of America."
Delivering the invocation, civil rights activist Myrlie Evers-Williams asked for blessings for "all who contribute to the essence of the American spirit, the American dream."
"We ask for your guidance toward the light of deliverance," she said.
Poet Richard Blanco read his ode to "Everyday of the Everyman and Everywoman" that included a reference to the massacre at Sandy Hook Elementary School in Newtown, Conn., when he spoke of the "20 children marked absent today and forever."
In his benediction, the Rev. Luis Leon of St. John's Church in Washington, asked that the elected leaders be filled "with love of truth and righteousness and serve the nation ably and do your will."
Obama and Biden then went to lunch at Statuary Hall, where the menu included foods from New England and the Upper Midwest.