It is Luther's response to Desiderius Erasmus's "Diatribe on Free Will, " written in his direct and unique style, combining deep spirituality with humor. Luther writes powerfully about man's depravity and God's sovereignty. The crucial issue for Luther concerned what ability free will has, and to what degree it is subject to God's sovereignty. For Luther, this key issue of free will is directly connected to God's plan of salvation. Is man able to save himself, or is his salvation entirely a work of divine grace? This work is vital to understanding the primary doctrines of the Reformation and will long remain among the great theological classics of Christian history.