On the 10th anniversary of 9/11, President Obama urges Americans to reclaim the sense of unity and “common purpose” that brought the country together after the deadly attacks.

“The worst terrorist attack in American history also brought out the best in our country,” the president writes in a USA Today op-ed. “This is the true spirit of America. We must reclaim this anniversary – the ordinary goodness and patriotism of the American people and the unity that we needed to move forward together, as one nation.

“As a nation, we face difficult challenges, and as citizens in a democratic society, we engage in vigorous debates about the future. But as we do, let’s never forget the lesson we learned anew 10 years ago – that our differences pale beside what unites us and that when we choose to move forward together, as one American family, the United States doesn’t just endure, we can emerge from our tests and trials stronger than before,” Obama writes.

The president admits “that the last decade has been a challenging one for our country” but says today “our country is more secure and our enemies are weaker.

“The perpetrators of those attacks wanted to terrorize us, but they are no match for our resilience,” he writes. “While we have delivered justice to Osama bin Laden and put al Qaeda on the path to defeat, we must never waver in the task of protecting our nation.”

The president also reflects on his own  experience on that day. “Like every American, I’ll never forget how I heard the terrible news, on the car radio, on my way to work in Chicago,” he writes. “Yet like a lot of younger Americans, our daughters have no memory of that day. Malia was just 3; Sasha was an infant. As they’ve grown, Michelle and I faced the same challenge as other parents in deciding how to talk with our children about 9/11.” The president notes that one of the things he and his wife have told their daughters about that day is how the attacks united the country.

Obama will commemorate the anniversary by visiting the three locations where lives were lost. On Sunday, the president and first lady will participate in events at ground zero in New York City, in Shanksville, Pa., and at the Pentagon in northern Virginia.

“Ten Septembers have come and gone since that awful morning. But on this 10th anniversary of the 9/11 attacks, we are summoned once more to honor those we lost by keeping our country strong and true to their memory,” Obama writes.