As a young man, Lincoln identified religion as a balm for life’s various afflictions. His close friend Joshua Speed remembered Lincoln as saying that the most ambitious man could see every hope fail, but the earnest Christian could never fail, because fulfilment lay beyond life on earth.

Lincoln has long been well known as an infidel, or a dissenter from the Christian orthodoxy. But while doubts have often been mistaken for lack of interest in religious matters, the reverse is probably true. Many of history’s greatest believers have also been the fiercest doubters. “It is hard to imagine what religious tradition would be,” says scholar Jennifer Michael Hecht, the author of Doubt: A History, “if there weren’t people looking up and saying that they disagreed with what had come before.”

According to Isaac Cogdal, a contemporary of Lincoln’s who often talked theology with him, “His mind was full of terrible Enquiry.” The inquiry seems to have intensified around points of stress in Lincoln’s life, like his desperate breakdown in 1841, when he sank so deeply into depression that his friends feared for his life.

“I am the most miserable man on this earth,” Lincoln wrote in the midst of his despair. That summer, his friend Speed took him to his family estate in Kentucky to convalesce. There, Speed’s mother recommended the Bible, calling it the best cure for the ‘Blues’. “Lincoln said that he was sure she was right — “could one,” he said, “but take it according to the truth.” — Beliefnet.com