Martin Luther's two kingdoms doctrine is inseparable from his study of the Bible. The sources of this doctrine can be roughly divided into three parts: Paul's epistles in the New Testament provide the original thoughts for this doctrine; Genesis provides specific examples to illustrate this doctrine; The annotations of the Psalms and the Song of Songs are the perfection and supplement to this theory. When faced with the text of the Bible, Luther adopted a different hermeneutic approach from the early church fathers and medieval scholastic theologians, emphasizing that "the Bible is its own interpreter" while responding to the social concerns of his time. His two kingdoms theory raised the status of a secular state and laid the foundation for modem European democratic politics.