On Sept. 10, 2001, I took a late-evening flight out of Chicago. It was a routine trip. As I look back on that night now, I am struck by how easy it all was. Security at the gate was lax. No one asked for a photo ID.

When I awoke to the tragic news of the attacks the next morning, I was reminded of a Friday afternoon in November 1963 when the school principal interrupted our spelling quiz to tell us that President Kennedy had been assassinated. The time before and after these moments is separated by a wall. Sept. 10 feels like a foreign country, inaccessible, unrecognizable.

Sept. 11 pierced our national illusions of invulnerability and immortality the way those planes pierced the clear, blue New York sky that morning.

The attacks confronted each of us with a sobering truth: In this life, there are no guarantees.

The five years since 9/11 have been a time of national soul searching, of asking difficult questions about the presence of evil in the world, or how in the name of religion so much hate and violence could be unleashed. And while we may not be able to measure whether the world is less safe than it used to be, the world feels less safe.

The conclusion could be reached that 9/11’s legacy is one of despair. Not so. The most important lesson to be drawn from that fateful day leads us toward hope.

John Labriola was one of the Port Authority employees who was helping to lead office workers down a stairwell of the north tower of the World Trade Center. He happened on that day to take a photograph of a young fireman ascending the stairs with his eyes wide open, perspiring, hauling gear. All this was taking place in a building that momentarily was about to collapse.

The young fireman escaped with a minute to spare, as did Labriola.

But what Labriola wrote went beyond what any photograph could capture:

“The one conclusion I came to on 9/11 is that people in the stairwell were in a state of grace. They helped each other. They didn’t panic. Most people are basically good. I knew this, with certainty, because I had gone through the crucible.”

On that day, race, religion and rank didn’t matter. People rose to their better natures, and in their own fragmentary way, were incarnate for the one who is above every name, who is owned by no tribe, who seeks love, peace and justice for all.

In the end, we will not be defined by how we lived our lives before 9/11, but by how we live our lives from now on. Let us pledge to live lives of purpose for others. Let that be our 9/11 legacy.