President Obama in Oslo

Accepting the Nobel Peace Prize on Thursday, President Obama gave the speech he needed to give, but we suspect not precisely the one the Nobel committee wanted to hear.

Mr. Obama was appropriately humble. He said that “compared to some of the giants of history who have received this prize,” his accomplishments “are slight” and suggested that he had been chosen not so much for what he had done but for what he is expected to do.

He then acknowledged that most of what he called “the considerable controversy” surrounding his selection came from the fact that he is “the commander in chief of the military of a nation that is in the midst of two wars.” He made no apologies for that.

In a speech that was both somber and soaring, he returned again and again to Afghanistan, arguing that the war was morally just and strategically necessary to defend the United States and others from more terrorist attacks.

In a moving passage, he invoked the memories of Mahatma Gandhi and the Rev. Dr. Martin Luther King Jr., saying that without Dr. King’s vision, leadership and sacrifice, he never would have been standing at that lectern in Oslo.

But he said he could not be guided by their examples alone. “For make no mistake: Evil does exist in the world. A nonviolent movement could not have halted Hitler’s armies. Negotiations cannot convince Al Qaeda’s leaders to lay down their arms.”

In his introduction, the chairman of the Nobel committee, Thorbjorn Jagland, made only a brief, forbearing reference to Afghanistan. He made clear that Mr. Obama was chosen because of his commitment, and early steps, to unwind the worst policies and abuses of George W. Bush’s presidency. He pointed to Mr. Obama’s embrace of “multilateral diplomacy,” his offer to negotiate with Iran, his decision to ban torture, his efforts to revive arms control negotiations and address global warming. “President Obama is a political leader who understands that even the mightiest are vulnerable when they stand alone,” Mr. Jagland said.

It is a great relief to hear an American president described with such hope and respect. In his speech, Mr. Obama recommitted himself to those policies and principles, warning that “we lose ourselves when we compromise the very ideals that we fight to defend.”

What struck us most is how often Mr. Obama used the war in Afghanistan to make his points. He said that even as the United States confronts “a vicious adversary that abides by no rules,” this country must remain “a standard-bearer in the conduct of war.”

While he reserved the right to act unilaterally in a world where threats are “more diffuse and missions more complex,” he said, “America alone cannot secure the peace. This is true in Afghanistan.” And he directly challenged the widespread ambivalence and aversion toward the war in the United States and in Europe. “The belief that peace is desirable is rarely enough to achieve it,” he said.

When he announced his plan to send an additional 30,000 troops last week, Mr. Obama’s speech was well argued but sounded more like a legal brief than an exemplar of presidential oratory. At the time, he was coming out of months of difficult internal debates and girding himself for the skepticism and disappointment of many members of his own party.

On Thursday in Oslo, Mr. Obama argued his case far more eloquently.

We’ll leave it to the philosophers to debate what is and what is not a just war. But we agree that this war is a very difficult but necessary one.

We also know that there is no chance at all of winning it, and the broader fight against terrorism, unless the United States hews to international standards and upholds its own ideals. That is Mr. Obama’s promise and his challenge going forward.