Pro athletes in the NFL will again band together on Sunday during the national anthem to show solidarity for teammates protesting racism and injustice. In one sense, they are protesting against those who would deny them the ability to protest.

In another sense, though, they are sending a message to all of us  — one not of division but of inclusion. By taking a knee, locking arms or remaining in the locker room, they are forcing viewers — we, the people — to consider what we invest in symbols such as the flag and the national anthem and why we tend to get upset when they are used as objects of protest.

In short, these athletes are reminding us of the civil religion that binds us together, even when politics or the actions of our fellow citizens and leaders let us down. In the end, our nation is held together as much by a faith in the idea of America as by the laws that govern it. Without testing the legitimacy of national myths and symbols and challenging our nation to be better through protest, we risk letting partisanship and demagoguery define the meaning of America.

Civil religion describes the complicated faith Americans have in their nation. It is composed of sacred symbols like the flag, songs like “America the Beautiful” and hymns like the anthem. It is enshrined in texts like the Constitution and Declaration of Independence and celebrated on holidays like Memorial Day, Veterans Day or the Fourth of July. It can be found in prophetic figures like the founders and consecrated battlefields like Gettysburg and Vicksburg. And it appears in phrases like “In God We Trust” on money and “under God” in the Pledge of Allegiance.

While elections can be moments of reckoning in civil life, and houses of worship can pass religious judgment on the nation, there is a space in between God and the ballot box in which national symbols become sites of contest. That is where civil religion exists. Civil religion keeps us honest about the pretensions of the nation, its people and, most importantly, its leaders.

Of course, that is precisely what irks President Trump and other politicians about the NFL protests. In calling for owners to fire players who failed to show due deference to the anthem, these politicians echo what the Rev. Martin Luther King Jr. referred to as “the prophesying of smooth patriotism,” the insistence upon grandiose expressions of love for America regardless of its moral failings.

The vitriol spewed about players and protests, then, plays on a tradition of popular laziness that accepts superficial quasi-deifications of national symbols, and tightly couples the flag and the military to brand virtually all dissent as unpatriotic.

But the way in which the protesting players are tapping into the American civil religion also has ample precedent. Fifty years before Colin Kaepernick sparked outrage by kneeling during the anthem, King enraged millions of Americans by protesting the war in Vietnam. His critics assailed him for his lack of patriotism, but in King’s mind, nothing could have been more patriotic than attempting to force Americans to cleanse the nation’s soul.

The diametrically opposed ways that King and his critics perceived his protests reminds us that the meaning of our national symbols and patriotism, as well as the essence of citizenship itself, are always contested, especially when the nation is bitterly divided politically.

Indeed, it was the tragedy of Vietnam that sparked the resurgence of interest in civil religion. In 1967, sociologist Robert Bellah wrote an essay titled “Civil Religion in America” in which he grappled with the moral quandary posed by Vietnam — which was ripping the nation asunder. Bellah hoped Americans would reject superficial injunctions to be more outwardly patriotic and instead develop a robust, principled project that united them in justice.

Like King, the protesting NFL players are embracing Bellah’s vision and seeking to push the United States toward achieving its ideals through an active, rather than passive, patriotism. But such patriotism requires Americans to first look critically at the beloved symbols of their nation.

San Francisco 49ers safety Eric Reid encapsulated this “tough love” patriotism, declaring “it should go without saying that I love my country and I’m proud to be an American.” But he added, quoting James Baldwin, “exactly for this reason, I insist on the right to criticize her perpetually.”

The NFL — and American sports in general — have wrapped themselves in the flag and the anthem, but that is an artificial and largely commercial intersection. Indeed, acts of saluting the flag, standing for the anthem, praising the founders or revering particular monuments can be meaningful and yet still reflect some of the more facile elements of American civil religion.

As we look more closely at what we expect from a nation built on contradictions — forced labor, land theft and inequality, on the one hand, and a foundational dedication to expansive rights, revolutionary idealism and almost permanent protest, on the other — we find ourselves at a crossroads.

Civil religion isn’t an automatic solution to this crisis. Unchecked and uncritically assumed, it might undermine principle, delegitimize protest, whitewash history and divide the nation. But a different type of embrace of civil religion is both possible and necessary.

Today, while the nation faces perpetual war with adversaries abroad and among Americans at home, it remains a nation for which we continue to pledge our allegiance, sing patriotic songs and sacrifice our lives. But those actions — some far more profound than others — only have meaning if we recognize that protest is vital to achieving our national ideals.