Grey Eminence by Aldous Huxley

A gripping biography by the author of Brave New World
The life of Father Joseph, Cardinal Richelieu's aide, was a shocking paradox. After spending his days directing operations on the battlefield, Father Joseph would pass the night in prayer, or in composing spiritual guidance for the nuns in his care. He was an aspirant to sainthood and a practising mystic, yet his ruthless exercise of power succeeded in prolonging the unspeakable horrors of the Thirty Years' War. In his masterful biography, Huxley explores how an intensely religious man could lead such a life and how he reconciled the seemingly opposing moral systems of religion and politics.