What is Christianity's proper role in American presidential politics? This question has gripped the 2008 campaign. From the dispute over the acceptability of Mitt Romney's Mormonism, to Mike Huckabee's musings about conforming the US Constitution more to the Bible and the controversy over Sen. Barack Obama's former pastor, the spiritual and secular realms have collided fiercely. Just this week, Senator Obama and Sen. Hillary Rodham Clinton fielded questions from US religious leaders at a special forum broadcast on CNN.
More broadly, arguments over public policies – from war to illegal immigration – are increasingly being infused with scriptural justifications.
The media, of course, relish such controversy. So do many religious leaders, who use the occasion to offer the "real" interpretation of what Scripture says about a particular issue. As a result, religion and politics aren't just mingling – they're being wedded to the same goal: redeeming America's body politic.
A largely Protestant nation that can trace its theological taproot to Martin Luther ought to know better. As the original Reformer, Luther understood how critical it was to separate church and state and, in a more important sense, the spiritual kingdom of Christ and the secular realm where God reigns in a hidden way through humans using reason as a guide.
That is not to say that Christians today shouldn't let their Christianity inform their political values and action. They should. But the Bible is not a political playbook. Christians, or adherents of any religion for that matter, should refrain from using holy text to fight politically over human concerns. Using Christian doctrine to push a political agenda is not just rude – it is a dangerous departure from the core message of Christianity: salvation by grace through faith.
Christ Jesus was not crucified to make society nicer or fairer; no, he suffered to redeem the believer from sin.
Did not Christ tell Pontius Pilate: "My kingdom is not of this world" (John 18:36)? Which of these seven words is so hard to understand?
Yet the clarity of Christ's statement hasn't stopped mankind from trying to bring heaven to earth ever since – mostly through political tyrannies of the collectivist utopian variety.
Luther understood these temptations. "The devil never stops cooking and brewing these two kingdoms together," he wrote, referring to the spiritual and the secular realms. With these words in mind, Lutherans – or at least Lutherans strongly committed to the confessional writings of their church – shake their heads over the misuse of Scripture in American politics on both sides of the political divide.
How, then, should Christians engage in political affairs? Through the language of reason in the framework of natural law.
Citing Paul, Luther reminded Christians that natural law is "written with the finger of God" on people's hearts, a fact to which their conscience "bears witness." Thus, Christians who want to publicly oppose the practice of abortion and same-sex marriage do not need to quote the Bible to do so. Instead, they can appeal to logic and universal principles that exist, not by man's decree, but by, as the Declaration of Independence puts it, "the Laws of Nature and Nature's God."
Sadly, natural-law thinking became unfashionable in the two centuries after Jean Jacques Rousseau. This philosopher behind the French Revolution extolled instead man-made "positive law," which was detached from the universal ethic usually attributed to divine authorship.
In this context it is worth noting how the 20th-century Lutheran theologian Dietrich Bonhoeffer judged the French Revolution, whose utopian dream was the liberation of man from all constraint. To the martyred Bonhoeffer, this Revolution was "the laying bare of the emancipated man in his tremendous power and most horrible perversity," a false liberation that leads only to man's self-destruction. He saw both Communism and Nazism as the French Revolution's heirs.
Natural law is the "operating system" in what Luther called the "left-hand kingdom," where God reigns in a hidden way "through good and bad princes," who in a democracy include the voters. In this secular realm, "reason is the empress," Luther said, describing reason as a gift from God that enables humanity to manage this temporal world.
Bonhoeffer considered the inability to distinguish between the spiritual and earthly kingdoms a major flaw of American theologies that manifest themselves as organized struggles against some particular worldly evil. "It is necessary to free oneself from the way of thinking, which sets out from human problems and which asks for solutions on this basis. Such thinking is unbiblical," he asserted. "The way of all Christian thinking leads not from the world to God but from God to the world."
Luther proclaimed a liberating message "that society need not be run by the Church in order to be ruled by God," according to the late William Lazareth, a former Lutheran bishop of New York. Yet too many Protestants have a hard time grasping the breathtaking implication of this insight.
To be sure, it would be desirable if more people turned to the Bible more often for everyday guidance. But the Gospel has nothing to say about traffic rules, illegal immigration, the price of gasoline, or the Iraq war.
The Gospel – the good news of salvation through Christ – is the Christians' highest good. Thus it is difficult to fathom why so many of them insist on exposing this magnificent treasure to public derision by using it for the wrong purpose. The Gospel can illume the believer's reason in his secular pursuits but is not meant to be a script for them.
Half a millennium after Luther nailed his 95 theses to the door of the Castle Church of Wittenberg, it makes sense to ponder his down-to-earth comment that in politics, as in all other aspects of secular life, Christians must act reasonably according to natural law. The Gospel has freed them to do just that; it must not be perverted into a weapon to be slapped around other people's heads.
• Uwe Siemon-Netto, a former religion editor for United Press International, is director of the Center for Lutheran Theology and Public Life in St. Louis. This essay was adapted from a longer version originally published by Christianity Today.