On Christian Liberty (Unabridged‪)‬

Martin Luther's On Christian Liberty is considered to be Luther's seminal work on the doctrine of salvation by grace through faith alone, and not through works. This short manifesto expounds on the nature of the freedom of a Christian, providing some of the principles that would become the foundation of the Protestant Reformation. It includes the concepts of "man's twofold nature" (the inner spiritual nature or the soul and the outer bodily nature of the flesh) and the importance of each individual being their own priest; thus establishing the foundation for the idea of the "priesthood of all believers".