The late Rev. Martin Luther King Jr. has long been hailed as a civil rights leader, but religious studies professor Lewis Baldwin said one aspect of his life has often been overlooked: the role of prayer.

"In order to understand him, you must begin, I think, with this idea of King as a spiritual leader," said Baldwin, author of the recent book, "Never to Leave Us Alone: The Prayer Life of Martin Luther King Jr."

"Dr. King always made it clear that his civil rights and political activities were an extension of his ministry."

As the nation marks the 25th anniversary of Monday's (Jan. 17) federal holiday honoring King, the scholar who has spent a quarter century chronicling King's cultural influences has focused on King's prayer life.

For King, personal prayer and public prayer were equally significant, the scholar said.

"Dr. King's personal devotional life was very, very important in giving him the courage and the determination to fight for justice," said Baldwin, who teaches at Vanderbilt University in Nashville, Tenn.

King would take "personal prayer retreats" and shut himself in a hotel room or pastor's study to pray, meditate and plan his next sermon or civil rights activities.

"But public prayer was important to him also because he understood prayer in that context as a form of creative energy," Baldwin said. "It was a way of motivating, affirming, reaffirming, empowering people in the context of the struggle for equal rights."

He writes that "prayer was King's secret weapon in the civil rights movement," a key to its success as people found the strength to continue despite arrests and killings.

King's prayers included a sense of perspective on the man and the movement he led. In a 1957 sermon at his Dexter Avenue Baptist Church in Montgomery, Ala., he said one of his daily prayers was, "Help me, O God, to see that I'm just a symbol of a movement."

Others were personal as well as corporate: "As we look within ourselves we are confronted with the appalling fact that the history of our lives is the history of an eternal revolt against thee," he prayed in a 1953 prayer broadcast from Atlanta's Ebenezer Baptist Church.

He sounded a similar tone later that year: "We realize that we stand surrounded with the mountains of love and we deliberately dwell in the valley of hate," according to the 2007 volumes of "The Papers of Martin Luther King Jr."

Prayer -- at mealtimes and before leaving for school -- was emphasized in King's childhood home, where he grew up the son and grandson of Baptist preachers. As a young married father, he continued prayer traditions when he was home with his own family.

King had what was perhaps the most transforming prayer experience in 1956, after a midnight call from a racist who threatened to kill him and destroy his home.

"He retreated to his kitchen and over a cup of coffee poured his heart out to God," Baldwin said.

King later preached a sermon about the experience, saying he had a vision of God telling him to "stand up" for righteousness and assuring him that he would always have God's companionship.

"He felt from that point on that he was never really alone," said Baldwin, who named his book after King's experience.

Baldwin, who heard King speak as a high school junior in Camden, Ala., said King's praying and preaching were intertwined.

"You can't talk about his preaching without talking about his prayer life because he engaged in prayer from the point of the preparation of the sermon," he said.

Often his prayers were brief, only one or two sentences in length.

"He had difficulty at times with those in the black churches who prayed on and on for minutes and minutes and minutes, repeating themselves," said Baldwin, 61. "He felt that prayer at that point becomes just an exercise in words and perhaps even meaninglessness."

King's prayers, influenced by the legacies of St. Francis of Assisi and nonviolence advocate Mahatma Gandhi, became a pioneering aspect of interracial and interfaith dialogue, Baldwin said.

"Dr. King was able to intersect into the civil rights movement Christians, Muslims, Jews, Protestants, Catholics and they all ... sang together and prayed together," Baldwin said.

More than four decades after King's assassination, Baldwin said King's focus on prayer has much to teach other social movements.

"Dr. King taught us about the importance of prayer, not only as a part of our own personal devotional life but ... also prayer must be a part of any movement for social action," he said.