United Flight 93 carried 40 passengers and crew when hijackers seized it as part of the attack on America. Through phone calls with people on the ground, several learned that hijacked airplanes had already struck the World Trade Center and the Pentagon. They understood that Flight 93 was part of the larger attack, took a vote, and decided to resist. As they prepared to move, telephone operator Lisa Jefferson heard Todd Beamer ask, “Are you guys ready? Okay. Let’s roll.”

They could not change what had already happened in New York and at the Pentagon, but they could still keep the hijackers from reaching Washington and killing more Americans.

The Gospel of John records Jesus Christ teaching, “Greater love hath no man than this, that a man lay down his life for his friends.” The passengers and crew of Flight 93 risked their lives for people whose names they would never know.

On the 25th anniversary of September 11, Americans should ask what those sacrifices require of us. America marks that anniversary in the same year it celebrates 250 years of independence. We are not only looking backward at the graves of those who gave their lives. We must decide whether we still possess the moral seriousness to preserve the country and the liberty their sacrifices helped protect.

As thousands of people descended from the World Trade Center toward safety, firefighters carrying equipment climbed toward those trapped above them. The Fire Department of New York lost 343 members that day. They climbed toward people they did not know while thousands moved in the opposite direction because other lives depended on them.

In Afghanistan, Navy Lt. Michael P. Murphy risked his life for his men. On June 28, 2005, Murphy led a four-man SEAL team fighting a much larger enemy force. The terrain prevented him from reaching headquarters from cover. In the face of “almost certain death,” Murphy “fought his way into open terrain” so he could call for help. Enemy fire struck him during the transmission, but he completed the call and continued fighting until he was mortally wounded, giving his life “for his country and for the cause of freedom.”

The sacrifices of September 11 and the war that followed carried forward an American duty older than the republic itself. Before independence had even been declared, Americans risked their lives for people and generations they would never know.

On April 19, 1775, Capt. John Parker assembled the Lexington militia as British regulars approached Concord. Parker later testified, “I immediately ordered our Militia to disperse and not to fire.” British fire killed eight Lexington militiamen and wounded ten. After Lexington buried its dead and tended its wounded, Parker rallied part of his company and attacked the retreating British column in the engagement now known as Parker’s Revenge.

At Bunker Hill, Dr. Joseph Warren died fighting before anyone could know whether colonial resistance would produce independence or defeat. Daniel Webster remembered Warren “pouring out his generous blood like water” before knowing whether it would fertilize “a land of freedom or of bondage.” Warren never saw the country his blood helped purchase. He died before anyone could know whether the colonies would win.

The men who declared independence had no assurance that the country they were creating would survive. When the Continental Congress adopted the Declaration on July 4, 1776, its members pledged to one another “our Lives, our Fortunes and our sacred Honor.” They rejected allegiance to the British Crown while British forces were already at war with the colonies and put their lives, property, reputations, and futures behind a country whose survival no one could guarantee.

On July 3, 1776, John Adams told Abigail Adams that Americans should commemorate independence with “solemn Acts of Devotion to God Almighty.” He also acknowledged the “Toil and Blood and Treasure” required to maintain the Declaration and defend the states. Even so, he believed “Posterity will tryumph in that Days Transaction.”

We are the posterity Adams had in mind, living under a liberty we did not create but inherited.

That inheritance includes rights, but rights alone cannot sustain a free country. Rights tell us what others may not take from us. Duty tells us what we must sometimes give. A constitutional republic needs both. Citizens cannot preserve it by asking only what government, country, neighbor, church, employer, or family owes them. They must also understand what they owe in return.

Jordan Peterson ties that duty to the survival of civilization. “Sacrifice is by necessity the foundation of civilization,” he has argued, because marriage, family, community, country, and the future require people to surrender immediate gratification.

In Christian teaching, that willingness to sacrifice for another is charity. Elder David A. Bednar recently taught that “charity is the very essence of the ‘end’ toward which we are enduring—becoming new creatures in Christ.” Charity is more than generosity or kindness. It is self-giving love willing to bear a cost for another.

God gave us agency, and charity has meaning because we choose it. We may protect ourselves or accept risk for another; keep what is ours or give it up because someone else needs it more.

Most Americans will never face a hijacked airplane, a burning tower, or an Afghan mountainside. For most of us, sacrifice takes quieter forms. Parents put children before themselves. Servicemembers leave their families to defend people they will never meet. Citizens defend what is right even when doing so costs them something.

Those duties reach public life as well. Americans now fight over whether the nation may control its borders, preserve its constitutional inheritance, teach its history, expect allegiance from its citizens, and pass that inheritance to the next generation. Those disputes force Americans to decide whether having a country imposes duties as well as confers benefits.

We should remember the 2,977 people murdered on September 11, say their names, tell our children what happened, and honor those who bore the cost of that day and the years that followed. If we honor what they gave, we must also decide what we will do with the country and liberty they helped preserve.

The men on Lexington Green could not know us. Joseph Warren never saw American independence. Many firefighters climbing the towers went to save people they had never met. The passengers of Flight 93 could not know the people on the ground their resistance might spare, and Michael Murphy could not know the Americans who would someday read his name. They did not need to know us for us to inherit what they preserved.

We are the people they sacrificed for. On the 25th anniversary of September 11, we must decide what we will preserve for those who come after us. As America marks 250 years of independence, the measure of our generation is whether we still possess the character to leave them a free country, knowing they will never know our names.