I was on the National Mall yesterday when Barack Obama took the oath of office and gave his inaugural address, and the mood was both delighted and solemn. The densely packed crowd alternated between loud cheers and reverent silence as Obama spoke.

Our new president was blunt in his description of our current situation, reminding us that we’re at war, our economy is badly weakened, and our healthcare, education, and energy systems are far from where they should be (full text here). But he expressed confidence that we can meet these challenges:

Now, there are some who question the scale of our ambitions, who suggest that our system cannot tolerate too many big plans. Their memories are short, for they have forgotten what this country has already done, what free men and women can achieve when imagination is joined to common purpose and necessity to courage.

What I found most heartening about the speech was not just this faith in our country’s abilities, but the “common purpose” that Obama outlined, which included these:

The nation cannot prosper long when it favors only the prosperous. The success of our economy has always depended not just on the size of our gross domestic product, but on the reach of our prosperity; on the ability to extend opportunity to every willing heart — not out of charity, but because it is the surest route to our common good.

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To the people of poor nations, we pledge to work alongside you to make your farms flourish and let clean waters flow; to nourish starved bodies and feed hungry minds. And to those nations like ours that enjoy relative plenty, we say we can no longer afford indifference to the suffering outside our borders, nor can we consume the world’s resources without regard to effect. For the world has changed, and we must change with it.

In the coming weeks, there will be a lot of discussion about the size and composition of the stimulus package and other tools for improving our grim economic situation. As we debate the details, we can’t lose sight of these goals: extending prosperity and opportunity to all, working for food and clean water worldwide, and using resources responsibly. This is a common purpose worthy of the courage, creativity, and determination that we are ready and willing to employ.