Martin Luther's A Treatise on Christian Liberty, published in 1520, comments on the paradoxes inherent in Christian freedom. Luther states the apparently contradictory precepts:
A Christian is a perfectly free lord of all, subject to none. A Christian is a perfectly dutiful servant of all, subject to all.
He then discusses the twofold nature of man: the soul and the body. The freedom which matters is the soul's freedom, which is invisible. Someone who is physically free may be spiritually in bondage, which is a far more serious condition than being in prison. It is faith in Christ that makes the Christian spiritually free.
Although the Christian is justified by faith rather than by good works, Luther says that he will perform good works in any case, serving others because he wishes to do so. Those who have not been justified by faith will continually quarrel over matters that concern only the outward man, such as ceremonies and forms of worship, while the faithful will be free from such petty disputes.