Washington ? Sen. Sam Brownback’s journey from a family farm in tiny Parker, Kan., to the halls of the Senate and a campaign for the GOP presidential nomination has been as much a spiritual awakening as a political one.

In his new book, “From Power to Purpose: A Remarkable Journey of Faith and Compassion,” the Kansas senator recalls a seminal moment in 1997, shortly after he was elected to the Senate, when the chaplain who led his Bible study class suggested every lawmaker has just one constituent: God.

That led to Brownback’s transformation as a self-proclaimed “compassionate conservative” and laid the foundation for his commitment to fighting poverty, disease and injustice around the world.

“From then on, I was going to think seriously about that ‘constituency of one’ in every decision,” writes Brownback, a convert to Catholicism.

Religion permeates nearly every corner of Brownback’s book, written with Jim Nelson Black and officially slated for release Tuesday. His soul searching began in 1995, hastened by two dramatic events in his personal life. His marriage was in real trouble – he was “on track” to getting divorced – as he devoted all his waking energy to furthering the conservative agenda that fueled the Republican takeover of the House in 1994.

Even more traumatic was his 1995 bout with cancer and surgery to remove malignant melanoma from his right side. Brownback says he finally found peace when he resolved to devote himself to God.

“One night I got down on my knees and said ‘OK, Lord, that’s it. I give up. It’s all Yours,'” Brownback writes.

His religious awakening eventually led him to make a stunning apology to Hillary Rodham Clinton a few years later during a Senate prayer breakfast. Brownback told the audience that he used to have a “hatred for Bill and Hillary” because of their politics. He later spoke directly to Mrs. Clinton and apologized to her, saying he realized “those thoughts of hatred were wrong.”

The book is bound to please Brownback’s other constituency – religious conservatives who play a key role in the Republican presidential primaries.

Brownback’s well-known opposition to abortion takes a prominent role in the book as he defines his belief in a “culture of life.” The concept that every person everywhere has dignity and worth has led Brownback to decry the legacy of legalized abortion, as well as embryonic stem cell research and assisted suicide.

He often equates the anti-abortion movement with the fight against slavery, fueled by the religious passion of abolitionists such as John Brown in Kansas. Brownback describes his fascination with Brown and his admiration for legendary British lawmaker William Wilberforce, who led the fight to abolish slavery in England.

Unlike former Sen. John Danforth, a Missouri Republican whose book last year argued that Christianity has become a polarizing force in U.S. politics, Brownback celebrates the political awakening of evangelicals and their influence in conservative politics.

A key platform of Brownback’s campaign is “renewing the family and rebuilding the culture.” The book highlights his push to renew the institution of marriage, for example, through his idea to provide monetary incentives for people to get married.

He also reaffirms his well-publicized stance against gay marriage, arguing that same-sex unions hurt the institution of marriage and lead to more births out of wedlock.

“If the culture silences goodness in the name of tolerance and celebrates vice instead of virtue, it enables and encourages wickedness,” Brownback writes. “We reap what we sow.”

Nearly half of the book is devoted to Brownback’s ambitious international agenda, which has set him apart from other presidential candidates.

That includes highlights of his key role in the passage of legislation to fight international sex trafficking and his leadership in the call to end genocide in the Darfur region of Sudan.