Classicly

Tolstoy's The Kingdom of God Is Within You is a fascinating work, from both a religious and a historical perspective. In the book he outlines a radical reorganization of society based on a literal translation of Christianity. Not in a Holy Roller sort of way but in an actual "What would Jesus do?" sort of way, banning war and murder and following the teachings of Christ to a 'T'.

This book would have a profound effect on Gandhi, who after reading it was turned on to the idea of liberating his people from British rule. Tolstoy wrote to Gandhi in a letter titled "A letter to a Hindu," in which he details the notion that only by using love as a weapon through passive resistance would his people be set free. Eventually this would come true as Gandhi applied the teachings of non-violence to his revolution. The two had an ongoing correspondence, and just before his death Tolstoy wrote again to the Hindu - which was the last letter the Russian literary master ever wrote.