The crown jewel of Martin Luther’s writings, his magnum opus, is The Bondage of the Will. Of course, that’s next to his work in translating the Bible into German. Luther himself considered The Bondage of the Will one his most important works. At the end of his life, Luther said, “You can burn all of my books except for two, The Bondage of the Will and the Small Catechism.”

The Bondage of the Will was published in 1525. At one point, Luther called it “the centerpiece of the Reformation.” There are two things going on in The Bondage of the Will that are worth noting. One is its theological emphasis and the other is its methodological emphasis.

First, the theological emphasis. Luther wrote this treatise in an engagement with the great Renaissance humanist Desiderius Erasmus. Erasmus helped set the stage for the Reformation by publishing his Greek New Testament in 1516. He was also the author of In Praise of Folly, a great satire of the Roman Catholic Church of the day. But Luther did not see him as embracing the doctrines of the Reformation. Luther applauded his criticism of the church but said, “I fear that the dear Erasmus does not go far enough in embracing the truth.” Erasmus thought Luther was wrong and challenged him on his teaching on the will. Erasmus taught that the will is free and that Scripture leaves a lot of wiggle room when it comes to God’s sovereignty and our freedom. Luther challenged that and made the case that the will is bound. He said that we are part of “Adam’s sinful lump.” This is an expression that he got from Augustine that means that we are totally depraved. That is, we all are fallen, but also every part of us, our whole being, including our intellect and our will, is fallen. And so, our will is not free; it is bound to sin. And God must do a redeeming work in us.

Second, there is the methodological emphasis, and this comes through in the preface. Erasmus was about equivocating rather than clearly asserting—he talked about wiggle room—and Luther said, “For it is not the mark of a Christian mind to take no delight in assertions. On the contrary, a man must delight in assertions to be a real Christian. And by assertion, in order that we may not be misled by words, I mean a constant adhering, affirming, confessing, maintaining, and an invincible persevering.” He went on to say, “I am speaking about the assertions of those things that have been divinely transmitted to us in the sacred writings. We don’t assert when it comes to man-made doctrines but we must assert when it comes to the biblical doctrines.” And that assertion involves confessing, maintaining, teaching, and invincibly persevering. In the preface, Luther continued, “Let skeptics and academics keep well away from us Christians but let there be among us asserters twice as unyielding as the stoics themselves.” Then he said, “Nothing is better known or more common among Christians than assertion. Take away assertions and you take away Christianity.”

So, Luther made a very important theological point in this treatise: Scripture teaches the bondage of the will. He also made a very important methodological point in this treatise: Christians assert. In fact, they delight in it. That’s Luther on the bondage of the will and on assertions.