By John Blake, CNN

(CNN) - David O'Brien couldn't help himself. After the September 11 terrorist attacks, he became obsessed.

O'Brien read the stories of 9/11 victims over and over, stunned by what he was discovering.

He read about the firefighters who marched up the smoke-choked stairwells of the World Trade Center, though many knew they could die; the beloved priest killed while giving last rites as the twin towers collapsed; the passengers on hijacked planes who called their families one last time to say, "I love you."

"I was obsessed with these stories," says O'Brien, a Catholic historian at the University of Dayton in Ohio. "There were so many stories of self-sacrifice, not just by the first responders, but by people fleeing the building. There was this revelation of goodness."

O'Brien saw an Easter message in 9/11 - good rising out of the ashes of evil. Yet there were other religious messages sent that day, and afterward, that are more troubling, religious leaders and scholars say.

September 11 didn't just change America, they say. It changed the nation's attitude toward religion. Here are four ways:

1: A chosen nation becomes a humbled one.

One man died because he arrived early to work. A woman died because she decided to take a later flight. The arbitrary nature of some of the deaths on 9/11 still sticks with many Americans today.

Yet this is what life is like for billions of people on the planet today, some religious leaders say. A random event - a car bomb, a stray bullet - can end their lives at any minute.

Most Americans had not lived with this vulnerability until 9/11, says Mathew Schmalz, a religion professor at the College of the Holy Cross in Massachusetts, who once lived in Karachi, Pakistan.

"We had this sense of specialness and invulnerability that 9/11 shattered," he says. "Given that a large section of the world's population deals with random violence every day, one of the outcomes of 9/11 should be a greater feeling of solidarity with people who live in cities like Karachi in which violence is a part of everyday life."

Recognizing that vulnerability, though, is difficult for some Americans because of how they see their country, Schmalz and others say.

They say Americans have long had a triumphalist view of their place in history. Certain beliefs have been engrained: Tomorrow will always be better; we're number one. The term "American" even reflects a certain arrogance. It casually discounts millions of people living in Central and Latin America.

The 9/11 attacks, though, forced many Americans to confront their limitations, says Rev. Thomas Long, a nationally known pastor who has been active in post 9/11 interfaith efforts.

"We're losing the power of the American empire and becoming more a nation among nations," says Long, a religion professor at Emory University in Atlanta. "The world is a much more dangerous and fragile place economically."

How Americans cope with their loss of power is ultimately a theological question, Long says. It's the same question the ancient Hebrews confronted in the Old and New Testaments when they faced national calamities.

The chosen people had to learn how to be humble people, Long says. Americans face the same test today.

"The challenge for every faith tradition is going to be helping people grieve the loss of an image of America that they once had," he says, "and acquire a modern understanding of ourselves on the world's stage."

2: The re-emergence of "Christo-Americanism."

Before 9/11, if you asked the average American about Ramadan or sharia law, they probably would have given you a blank look.

Not anymore. The 9/11 attacks prompted more Americans to learn about Islam. Books on the subject became best-sellers. Colleges started offering more courses on Islam. Every cable news show suddenly had their stable of "Muslim experts."

More Americans know about Islam than ever before, but that hasn't stopped the post-9/11 Muslim backlash. The outrage over plans to build an Islamic prayer and community center near ground zero; the pastor who threatened to burn the Quran; conservative Christian leaders who called Islam evil - all occurred as knowledge of Islam spread throughout America, scholars says.

"One of the sobering lessons of the decade since 9/11 is that religious prejudice is not always rooted in raw ignorance," says Thomas Kidd, author of "American Christians and Islam."

"Some of America's most vociferous anti-Muslim critics know quite a lot about Muslim beliefs, but they often use their knowledge to construe Islam in the worst possible light."

Many of these public attacks against Islam were encouraged by conservative Christian leaders such as Rev. Franklin Graham, the son of Rev. Billy Graham, who called Islam "wicked," and Pat Robertson, the Christian broadcaster who declared that "Islam is not a religion," says Charles Kammer, a religion professor at the College of Wooster in Ohio.

Kammer says Graham and Robertson helped fuel the rise of "Christo-Americanism," a distorted form of Christianity that blends nationalism, conservative paranoia and Christian rhetoric.

"A segment of the religious community in the United States has been at the forefront of an anti-Islamic crusade that has helped to generate a climate of hatred and distrust toward all Muslims," says Kammer.

Other strains of Christo-Americanism have swept through America before.

After 9/11, some political leaders said terrorists hated the U.S. because of "our freedoms." But America's record on granting those freedoms to its citizens is mixed, says Lynn Neal, co-editor of the book, "Religious Intolerance in America."

In the 19th century, the U.S government passed numerous laws preventing Native American tribes from practicing their religion. Mormons were persecuted. Roman Catholics were once described as disloyal, sexual deviants, Neal says.

"Religious intolerance is not a new feature of the American landscape. Despite being the most religiously diverse nation on earth, despite having a first amendment that protects religious rights...we as a nation and as citizens have often failed to live up to those ideas."

3: Interfaith becomes cool.

Interfaith dialogue - it's not the type of term that makes the heart beat faster.

Before 9/11, interfaith efforts were dismissed as feel-good affairs that rarely got media coverage. The 9/11 attacks changed that.

Interfaith events spread across the country. Mosques and temples held joint worship services. Every college campus seemed to have an interfaith dialogue. The Obama White House launched a college interfaith program.

Becoming an interfaith leader is now hip, some say.

"A generation of students is saying that they want to be interfaith leaders, just like previous generations said they wanted to be human rights activists or environmentalists," says Eboo Patel, who founded the Interfaith Youth Core in 2002.

Patel says at least 250 colleges have signed up for the White House interfaith program, which he helped design. The program encourages students of different faiths to work together on service projects.

"These young leaders will make interfaith cooperation a social norm in America, similar to multiculturalism and volunteerism," Patel says.

These new leaders include people like Sarrah Shahawy, a Muslim-American medical student at Harvard University and the daughter of Egyptian immigrants.

After 9/11, Shahawy says she felt the responsibility to educate people about Islam. She became an interfaith leader at the University of Southern California, where she noticed a steady increase in student participation in the years after the attacks.

Shahawy says her generation is drawn to interfaith efforts because 9/11 showed the destructive potential of any exclusive claims to religious truth. The 9/11 hijackers carried out their attacks in the name of Islam, but Muslim religious leaders and scholars said that the terrorists' actions did not reflect Islamic teachings.

"For one religious group to claim a monopoly on truth should be obsolete," she says. The interfaith movement doesn't teach people that all religions are the same, she says.

Shahawy calls herself a proud Muslim. "But for me, there's beauty and truth to be found in many different religions."

4: Atheists come out of the closet.

There's one group, however, that sees little beauty in any religion.

Before 9/11, many atheists kept a low profile. Something changed, though, after 9/11. They got loud.

Atheist leaders such as Richard Dawkins, author of "The God Delusion," and Sam Harris, author of "The End of Faith," wrote best-selling books. Atheist groups launched national media campaigns with bold billboard messages such as "Christmas is a myth."

The pugnacious journalist Christopher Hitchens became the public face of a more combative form of atheism as he went on talk shows and lectures to defend not believing in God.

Criticism of all religion, not just fanatical cults, was no longer taboo after 9/11, says Daniel Dennett, a philosophy professor with Tufts University in Massachusetts.

"Atheist-bashing is now, like gay-bashing, no longer an activity that can be indulged in with impunity by politicians or commentators," Dennett says.

Atheists were driven to become more vocal because of the 9/11 attacks and America's reaction, says David Silverman, president of American Atheists. He says many atheists were disgusted when President George W. Bush and leaders in the religious right reacted to the attack by invoking "God is on our side" rhetoric while launching a "war on terror."

They adopted one form of religious extremism while condemning another, he says.

"It really showed atheists why religion should not be in power. Religion is dangerous, even our own religion," Silverman says.

Atheists are still the most disparaged group in America, but there's less stigma attached to being one, he says.

"The more noise that we make, the easier it us to accept us," Silverman says. "Most people know atheists now. They knew them before, but didn't know they were atheists."

Many Americans knew the people who perished on 9/11 as well, but they didn't know they were heroes until later, says David O'Brien, the Catholic historian who compulsively read the 9/11 obituaries.

O'Brien was so moved by the stories he read that he decided to write an essay for America magazine, a national Catholic weekly, entitled, "9/11 Then and Now."

He wrote: On 9/11, "Our people, my people, were tested and, for a shining moment ... they were found worthy."

He said many 9/11 victims didn't panic as their end drew near. They "thought not of themselves, but others ... when the chips were down." They saw themselves not as individuals, but as members of a "single human family."

So should we, he says, as we face new challenges 10 years later. The 9/11 victims aren't just heroes; they're our guides for the future, he says.

"The story is not over, not by a long shot," O'Brien wrote. "Look at all the love that day. Love can still write another chapter and keep hope alive for a better future. The meaning of 9/11 lies ahead, and it's in our hands, and maybe in our hearts.'