Obama answers the question: Why are you a Christian?

President Barack Obama walks into the East Room of the White House with Father Vien Nguyen in Washington, May 24, 2010.

ALBUQUERQUE, New Mexico (Reuters) - President Barack Obama spoke openly about his faith on Tuesday, describing himself as a "Christian by choice" while reiterating his belief in the importance of religious tolerance.

Obama, who polls show many Americans think is a Muslim, was asked by a participant at a campaign-style New Mexico event why he was a Christian.

"It was because the precepts of Jesus Christ spoke to me in terms of the kind of life that I would want to lead -- being my brother's and sister's keeper, treating others as they would treat me," he said.

"And I think also understanding that, you know, that Jesus Christ dying for my sins spoke to the humility we all have to have as human beings -- that we're sinful and we're flawed and we make mistakes, and that we ... achieve salvation through the grace of God."

Obama rarely speaks about his faith, though many Americans use religious convictions as a criteria when choosing who to support for political office.

Obama said religion took on a stronger meaning for him as an adult.

"My mother was one of the most spiritual people I knew but she didn't raise me in the church. So I came to my Christian faith later in life," he said.

The president, who has voiced strong support for the right of Muslims to build a community center near the site of the September 11, 2001, attacks in New York, said he tried to express his religious beliefs through his job.

"I think my public service is part of that effort to express my Christian faith," he said.

"As president of the United States, I'm also somebody who deeply believes that ... part of the bedrock strength of this country is that it embraces people of many faiths and of no faith."

(Writing by Jeff Mason; Editing by Bill Trott)