Vägen Till Jerusalem by Jan Guillou

A coming-of-age historical novel set in 12th-century Scandinavia and the Crusader states, following Arn Magnusson, a noble youth whose passionate romance and a violent mistake lead to a sentence of enforced monastic penance; trained by monks and later absorbed into the Knights Templar, he is transformed by discipline and combat, traveling to the Holy Land where he matures into a skilled commander whose personal fate becomes entwined with the larger political, religious and military struggles of the era.