(RNS) Sean Tallon was nearing the end of his probationary training as a New York City firefighter when the two hijacked planes hit the twin towers of the World Trade Center on 9/11. Tallon, 26, ran up the North Tower to save others.

His family would never see him again.

"As my mom and dad said, `This isn't it,"' said his older sister, Rosaleen. "God has promised us an eternal life. That gave us the only comfort that could help us at that time."

Tallon and her parents, all faithful Catholics before 9/11, began going to Mass every day, sometimes more than once a day. They rebuilt a grotto at St. Barnabas Church in the Bronx to memorialize Sean. They composed a prayer in his honor.

"I don't know how people could get through this without faith," Tallon said.

For many 9/11 families, faith has been the lifeline that sustained them through the loss of a parent, child or sibling. But for others, faith was lost that day and has been a cold comfort in the years since. 

Hal French, who teaches the psychology of religion at the University of South Carolina, said such disparate reactions are entirely normal. French's stepdaughter survived the attacks at Ground Zero and found her comfort in family, he said. He's talked with Japanese survivors of the atomic bombs in 1945 who found solace in nature and the annual reappearance of the cherry blossoms.

"We're not all made from the same mold," he said.

Ruth Green also knows something about faith and 9/11. Green said it would be easier to cope with faith, but her religious faith disappeared that awful September day along with her son, 29-year-old Josh Aron, a newly married equities trader for Cantor Fitzgerald.

"My faith is shaken? Earthquake is a better word," said Green, who is Jewish. "In the end, I found myself saying, `What kind of God would allow this?"'

The 10 years that have passed since her son's death have not made surviving without him any more bearable. "Every year is another year I don't get to talk to Josh," she said.

But she still recites the Hebrew prayers for the dead for her son, and attends synagogue services. As she does every year, she will join her Manhattan congregation in reciting the names of those who died on 9/11.

"I can walk away from God," Green said. "But there's something about the rituals; I think Josh would be very upset that I didn't do them," she said. "I am drawn to them but I am not comforted by them." Lisa Miller, a scholar of religion and mental health at Columbia University, said losing faith is an understandable and normal reaction to tragedy, especially the loss of a child.

"There is nothing more devastating than losing a child," she said. "It's the most devastating psychological pain we can imagine. It's a violation against creation, a violation against life itself."

For some survivors, reclaiming lost faith has been an arduous journey. Susan Kim was in her office at the insurance company AIG near Ground Zero on 9/11 when she saw the fireball of the second plane hitting the South Tower.

In the street, she heard screaming and moaning and watched the tower fall. "I thought my children would never see me again," she said of her sons, who were preschoolers at the time.

Since then, Kim's struggle with post-traumatic stress disorder has kept her from returning to the job she loved; on days when the precariousness of life overwhelmed her, she could barely get out of bed.

She also lost her deep connection to Judaism, the religion of her husband's family, to which she had joyously converted before they were married. Going to synagogue drove her to tears, and the ritual Passover meals that she had once so eagerly prepared became a burden. "That day I lost that belief, I lost that comfort, that somebody upstairs a lot stronger than me would take care of me," Kim said.

A therapist earlier this year suggested that talking to a rabbi might help Kim return to the Jewish life she once enjoyed. Kim followed up, and is slowly reclaiming her religious self. She said she wants to pass her religion on to her sons, whom she has sent to Jewish schools.

"I want them to have God and some belief that's not going to change because we go to another continent," said Kim, whose family emigrated from South Korea when she was a teenager.

Miller said religious leaders can help rebuild a person's shattered faith, though it's not always an easy job.

"It's a crisis of faith, and one-on-one direct healing with clergy allows you to work through the pain," she said, "to deal with questions of faith and estrangement." 

And there are others -- those who should have been victims, but were spared by a twist of fate. And that has left them with a sense of renewed mission.

U.S. Army Col. Franklin Childress had recently been transferred to Washington and was supposed to have been at his desk in the Pentagon on 9/11. But he was home, waiting for movers to arrive after a clerical error delayed the delivery of his belongings.

"Everyone who was around my desk perished," he said. "A friend called me and said, `God works through incompetent transportation clerks too."'

In the days after 9/11, Childress was wracked by survivor's guilt, so he joined a Bible study group with other Pentagon employees. The gatherings became an important source of spiritual strength for Childress, a devout Christian.

Looking back 10 years later, Childress, now 50, says God must have wanted him to survive that awful day. He's used his chance to spend more time with his family, help others deepen their faith and appreciate his own life.

"We are not guaranteed another day," he said.