On September 11, 2001, Islamic terrorists on a murder-suicide mission flew commercial airliners into the two World Trade Center towers in New York City and the Pentagon in Washington. A fourth crashed in a Pennsylvania field.

The attacks against our country unified Americans in a sense that’s almost inconceivable today. Together, we mourned the 2,600 people killed in the collapse of the twin towers and were horrified to watch many leap to their deaths to escape the inferno.

We celebrated the courage of the emergency workers who rushed into the burning towers to save lives, and we grieved for 400 who died while bravely working to save others.

We admired the selfless courage of the passengers on United Flight 93 who, having learned that other planes had been crashed into buildings, confronted their hijackers, resulting in their plane ultimately crashing in a Pennsylvania field killing those on board but not killing hundreds more at the U.S. Capitol, its intended target.

Today, nearly one in three Americans has only a textbook knowledge of that day. Either they were not yet born or were too young to remember it. They should learn from us that 9-11 was a tragedy that pulled Americans together and often brought out the best in us.

We learned from 9-11 – as did the World War I and II generations – that even when America prefers to ignore the rest of the world, the rest of the world doesn’t ignore America.

The lessons of 9-11 exemplified courage, vigilance, and humility.

Every day, men and women in law enforcement and emergency services courageously risk their lives for our safety, as do those in the armed forces who defend our country and pursue our enemies in unfamiliar lands.

President Kennedy knew: “The cost of freedom is always high, but Americans have always paid it. And one path we shall never choose, and that is the path of surrender or submission.”

Today, we too easily surrender because we grow weary of reading bad news when Americans die in far-away places. At home, we choose to focus on the tragic misdeeds of a few in law enforcement rather than applaud the hard work and success of the many.

Vigilance reminds us that we cannot take our safety and security for granted. Oceans do not provide the security they did a century ago, especially not when terrorists and hostile governments can wreak havoc by hijacking a computer network.

Our enemies want to destroy us because they despise the liberty that America represents to the people they want to keep in chains. Those Americans who don’t comprehend our own exceptionalism – or claim that Americans are oppressors – are sowing seeds of self-destruction in our communities.

Vigilance means we must confront difficult choices with complicated answers, such as when is it necessary to confront our enemies abroad rather than wait for them to confront us at home?

George Washington, who spent eight long years leading Americans in the War for Independence, warned that “to be prepared for war is one of the most effectual means of preserving peace.”

Finally, 9-11 reminded us about humility. America remains “a shining city on a hill and a beacon of freedom” to billions abroad only if we accept the responsibility of liberty.

Americans have fought for the freedom of our own citizens and for the freedom of millions imprisoned, persecuted, and oppressed by tyrants across the globe. That’s our duty as the “Land of the Free and the Home of the Brave.” But today corporations, movie stars and athletes seek profits in communist China rather than stand for liberty and against the oppression of Hong Kong or China’s ethnic minorities.

Generations of Americans have recognized the role of Providence in securing “the blessings of liberty to ourselves and our posterity.” Rather than consume liberty as if it’s something to which we are uniquely entitled, we should honor this rare blessing by providing a lifeline to those you yearn for liberty anywhere.