There is a great upheaval in the evangelical church regarding how Christians should engage culture. The most common form of understanding, at least among American evangelicals, is the "Christ and Culture" model set forward by H. Richard Niebuhr. In this model the theory of "two kingdoms," namely the kingdom of Christ and the kingdom of the world, is central. This emphasis resulted in the strong secular and sacred distinctions that we find in fundamentalism, as well as in much evangelicalism.
This view is correct in so far as it reminds us of the very real enmity that exists between these two kingdoms until Christ comes again. While we live in both kingdoms now, and have responsibilities to both (cf. Romans 13) kingdoms, we are to give absolute homage to Christ alone. We will not bring in his kingdom by our efforts to transform the kingdom of the world. He stands over the world and thus must always remain our higher authority. Niebuhr referred to this thinking as "Christ-and-culture-in-paradox." The paradox explains the dominant way that most evangelicals, until the last twenty years or so, viewed politics, art, music, the media, etc. They might work in them, at least in a very limited sense, but they thought this work was not related directly to Christ's kingdom, which included missions, evangelism and church work. This is why we spoke of "calling" only in terms of missions and church ministry.
I believe this "pietistic" approach has been jettisoned by many conservative Christians on the political right without a thoughtful understanding of what they have rejected and what they now embrace in its place. I have grave concerns about this unthoughtful exchange. My own view is called, by Niebuhr, the "Christ-transforming-culture" model. This view is closer to Calvin and his theological heirs, such as the famous Dutch theologian Abraham Kuyper. The Christian right has embraced something like this view but without the nuances and theological vision behind it. The result is a chaotic mix of radicalism and political foolishness. In the words of my friend Andrew Sandlin these folks have no idea how this works because they do not understand "incrementalism" as the way things change for the best.
My primary criticism of the old view of two kingdoms, which I say again has much to commend it, is that it tends toward reinforcing the status quo. It allows unjust laws, social evil, bad policy and distorted cultural forces that will coarsen our way of life, to go unchecked by the light of Christ in the world. By dividing Christ and culture too comfortably into opposites what comes about is a radically interiorized religion that speaks to the heart of individuals without challenging them to do anything positive for the world in which they live. We became a colony of heaven, "just passing through" a sin stained world. Afterall, this world was headed for destruction so our role was only to pull sinners out of the world before the end came. The very people who advanced this kind of Christianity, from about 1900 to 1975, were the same people who created the Christian right. The good news is that multitudes of Christians now care about politics and culture. The bad news is that they do not understand the great harm they are doing in many cases. The damage being done is very serious. We desperately need good living models for how Christians live in this world as faithful disciples.