A few months after Luther created a media splash in Wittenberg with his Ninety-Five Theses, his monastic order – the Augustinians – honored his proposal for a disputation, or debate among theologians, on the propriety of the church's extension of indulgences. They gave him an opportunity to present his views at the order's leadership conference in Heidelberg in April 1518.

In preparation for the disputation, Luther prepared a new list of theses, staking out the arguments he would make. It was here, among these theses, that Luther first used a phrase that became a key concept for his theological emphases: the theologia crucis, or “theology of the cross.” The “theology of the cross” stands at the “crux” of Luther’s reformation. What did he mean by the phrase?

In the Heidelberg Disputation, Luther distinguishes between a “theology of glory” that “calls evil good and good evil” and a “theology of the cross” that “calls the thing what it actually is” (Thesis 24). This is rather cryptic, but when we put it together with the surrounding theses, we see that Luther means that a genuine Christian theologian is one who can see God at work in suffering and in the cross – choosing to get involved in humanity in the midst of our depravity and the ugliness of our sin – rather than preaching that humans can become “good” and thereby become worthy of interacting with God.

Luther is contrasting his “theology of the cross” with the type of scholastic theology that was dominant in his day, which he felt led people to believe that the way of salvation was through human merit – through perfecting a theological system or a legal code. That approach, he is arguing, takes people’s eyes off the cross in favor of things that look more appealing to us. The unsightly cross must remain the center, the crux, of Christianity because otherwise humans will seek salvation through their own righteousness rather than Christ’s righteousness. Christ sought to correct this disposition when claimed, in John 10, “I am the door;” “No one comes to the father but by me” (Thesis 23): apart from receiving Christ’s righteousness no one becomes righteous and worthy of approaching God’s glory. Thus, church leaders who convey an idea that humans can prepare themselves to step before God’s glory through their law-abiding acts – through their self-restraint or personal sacrifices to achieve their ideal of human ethics – are merely teaching people to gaze upon pleasing appearances; they are calling humans, who are still in a state of evil, good.

As Luther elaborates, it becomes apparent that he has in mind Paul's words to the Galatians: "Far be it from me to glory except in the cross of our Lord Jesus Christ" (Gal. 6:14). God must be sought where He has revealed Himself, and of all places, the glory of God was to be found on the cross of Golgotha – hidden in Christ’s suffering, in the Savior who was despised and rejected. The "theologians of glory" who Luther counters in the Heidelberg Disputation were those who, he thought, did not take seriously how profoundly we as humans are corrupted by sin, and thus how strongly we resist accepting a Savior who hung upon a cross. The "theology of the cross" is a re-orienting of our vision of both God and ourselves: we only get a grasp on reality, on our true human predicament – we only “call the thing for what it actually is” – when we come face to face with the ugliness of our sin and the humiliation that Christ experienced on the cross to extend his righteousness to us.

That message resonated for many people in the sixteenth century. In contrast, we live in an age in America that could well be characterized as a “guilt-free” culture. We praise the language of “self-expression” and “self-validation” and resent the language of guilt because it refers what goes wrong in the world back to us, and forces us to think of ourselves as sinners in need of forgiveness.

In 2010, I had the opportunity to witness a service at the Lutherans’ world-wide denominational conference in Stuttgart, Germany, in which church leaders asked for the forgiveness of Anabaptists and Brethren for past persecution. What they were doing, then, was something profoundly counter-cultural. We all recognized that the leaders of the Lutheran Church today have nothing to do with causing or advocating that past persecution, and Anabaptists and Brethren today are not in any place to claim they are suffering adverse consequences from that past persecution. But by asking for forgiveness nonetheless, the Lutherans acted as theologians of the cross; they reaffirmed our universal human condition as inheritors of guilt and thus drew our attention away from the reputations of our churches (a constant temptation for church historians like me) and instead brought the focus on Christ who acted as redeemer and mediator on the cross.

As we commemorate many Reformation anniversaries in the coming decade, this sets a strong basis to make Reformation history applicable to the church’s place in our culture today.