What is the theme in Bonhoeffer: Pastor, Martyr, Prophet, Spy by Eric Metaxas?

This is the book's primary thematic consideration, embodied and dramatized through the story of its central figure, Dietrich Bonhoeffer. The author places the circumstances and events of Bonhoeffer's life clearly within the context of the latter's belief, both heavily contemplated and decisively acted upon, that life was meant to be lived entirely in accordance to the will of God. The author and his work make it clear that for Bonhoeffer, that belief was unequivocal, and was to be rigorously applied in every conceivable circumstance - whether to travel, what feelings of attraction to a beautiful woman meant, whether to kill the man (Hitler) responsible for the deaths and ill treatment of millions