(NBC News) -- President Barack Obama issued a call to unity in his second inaugural address, urging the nation to move past the divisions that marked the last four years in politics and complete the work of living up to America's founding principles.
The president, in a speech that blended together post-partisan rhetoric and policy declarations, highlighted the progress made during his first term to end foreign wars and turn around the economy. But Obama said that there was much unfinished work ahead, and he used Monday's speech to urge political leaders to finally rise above bitter squabbling — a recurring theme of his first term, and a mark of how difficult it has been for Obama to live up to his 2008 vow to change Washington's business as usual.
"We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate," Obama said. "We must act, knowing that our work will be imperfect. 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 forty years, and four hundred years hence to advance the timeless spirit once conferred to us in a spare Philadelphia hall."
Obama and Vice President Joe Biden were sworn in by Chief Justice John Roberts and Supreme Court Associate Justice Sonia Sotomayor, respectively, shortly before noon; Monday's oath of office was ceremonial, following their formal, constitutionally-prescribed swearing-in on Sunday.
Monday's ceremonies coincided with the federal holiday honoring Martin Luther King, Jr. Obama nodded to the slain civil rights leader during his speech, and the nation's first African-American president used one of King's Bibles during today's inauguration.
The president's speech, though, strode between acknowledging the accomplishments of his first term and the new priorities for his second. The president begins his new term this week intent upon pursuing an ambitious agenda following his decisive re-election victory last November over Republican opponent Mitt Romney.
"Our journey is not complete," Obama said during one refrain in his speech.
Rebuilding the economy, strengthening entitlement programs for future generations and addressing the threat of climate change were among the initiatives upon which the president touched during his speech. Obama nodded toward other priorities, that were set to define his next four years in office: equal rights for gay and lesbian Americans, immigration reform that offers undocumented residents a pathway to citizenship and new rules to curb gun violence.
But as political leaders from both parties looked on from the inaugural platform, Obama avoided much of the hard-charging rhetoric of last year's campaign.
Romney, the erstwhile GOP nominee, spent Inauguration Day at his home in La Jolla, Calif., and a former aide to the said it was unlikely that the former Massachusetts governor would watch today's festivities.
Wisconsin Rep. Paul Ryan, Romney's running mate last fall, said today was not a day to emphasize partisan divisions.
"But today, we put those disagreements aside," Ryan said in a statement. "Today, we remember what we share in common."
To be sure, a variety of bruising political battles between Obama and Congress — in particular, a House of Representatives controlled by Republicans — loomed on the horizon. On Wednesday, Republicans said, they would vote on a measure to extend the nation's debt limit by a few months.
But much of Monday's ceremonies involved the pomp and circumstance of most inaugurations, leaving the hard edge of politics for another day.
There, Dr. Luis Leon, the rector of the church, led a series of "prayers for the nation," Washington Cardinal Donald Weurl led a Gospel reading, and an Alexandria, Va., rabbi offered a final blessing. Biden and his wife also attended the service.
Former Presidents Bill Clinton and Jimmy Carter were among the dignitaries in attendance during the oath-of-office ceremonies during late Monday morning. Celebrities including Jay-Z, Beyonce Knowles and Eva Longoria joined government officials on the inaugural platform, and attendees were treated to performances by the Brooklyn Tabernacle Choir and James Taylor, among other artists.
Obama would retreat to a traditional luncheon on Capitol Hill following the inaugural ceremonies before participating in the parade down Washington's Pennsylvania Avenue, which would consume much of the afternoon. The president and first lady will make their way to glitzy, black-tie inaugural balls later this evening before wrapping the whirlwind day of festivities.