Doctrine of The Two Kingdoms - On Secular Authority

Martin Luther's book, On Secular Authority, was an ardent expression of the principle of Liberty of Conscience. "Liberty of conscience" is the principle that forbids human authorities from coercing people's spiritual beliefs. In this book, Luther insisted that God requires voluntary religious beliefs. Compelled or coerced faith is insincere and must never be allowed. Luther insisted that "liberty of conscience" was one of Jesus Christ's principles. According to Luther, the civil government's role is simply to keep outward peace in society. The civil government has no business enforcing spiritual laws. "The laws of worldly government extend no farther than to life and property and what is external upon earth," Luther insisted. Echoing Luther, writing on religious liberty, Thomas Jefferson stated "The legitimate powers of government extend to such acts only as are injurious to others." Jefferson may not have had Luther specifically in mind, but was perhaps an heir to the Protestant tradition which gave birth to this sentiment. Addressing the question of whether the state should permit its citizens to believe religious views which are heterodox, Luther said, "heresy can never be prevented by force…heresy is a spiritual matter which no iron can strike, no fire burn, no water drown." In other words, it is folly to legislate and enforce religious beliefs.

Luther's articulation of the parameters of civil government was a monumental step in the development of the separation of church and state. He argued for a clear distinction between two separate spheres: civil and spiritual. This is known as the Doctrine of the two kingdoms. The civil sphere deals with man's physical life in society as he interacts with other human beings; in this, man is subject to human governments. The spiritual sphere deals with man's soul, which is eternal, and which is subject only to God. The Doctrine of the two kingdoms is articulated by Luther in these terms:

God has ordained the two governments: the spiritual, which by the Holy Spirit under Christ makes Christians and pious people; and the secular, which restrains the unchristian and wicked so that they are obliged to keep the peace outwardly…The laws of worldly government extend no farther than to life and property and what is external upon earth. For over the soul God can and will let no one rule but himself. Therefore, where temporal power presumes to prescribe laws for the soul, it encroaches upon God's government and only misleads and destroys souls. We desire to make this so clear that every one shall grasp it, and that the princes and bishops may see what fools they are when they seek to coerce the people with their laws and commandments into believing one thing or another.

Luther forbade Christians from allowing temporal rulers to meddle with their hearts in matters of belief, declaring that "if you give into him and let him take away your faith and books, you have truly denied God". However, in all temporal matters, subjects must obey and welcome true Christian suffering:

We are to be subject to governmental power and do what it bids, as long as it does not bind our conscience but legislates only concerning outward matters…But if it invades the spiritual domain and constrains the conscience, over which God only must preside and rule, we should not obey it at all but rather lose our necks. Temporal authority and government extend no further than to matters which are external and corporeal.