What is the role of government?

One of the more under-discussed issues in American politics is that of the role of government in addressing our favorite issues.  We might agree that education is good or that suburban sprawl is bad or that astroturf is evil, but how do we understand the role of government in regulating or addressing issues of education, sprawl, or astroturf?  This is a fundamental issue, one with which I wrestle considerably, but which I don't think gets enough air-time in our sound-bite political process.  Just becaue the power exists in government to do something, does it mean that government should necessarily do it?

Related to this point, I also wrestle with what Christians should seek from government.  If the Bible and the Christian tradition speak to people of faith, can we rightfully expect or demand of our (secular) government (of a religiously diverse nation) that it enact certain laws or policies "because the Bible says so"?  For exampe, the Bible expresses a deep concern for the plight of the poor, and calls people of faith to care for the needy.  Should Christians, then, implicate the government in responding to that faith-based call to serve neighbor?  Surely there are non-religious public policy reasons to serve the poor, and perhaps Christians should employ those arguments when calling on the government to act for the poor.  Again, just because the power exists in government to do something, does it mean that government should necessarily do it, and does it mean that Christians should seek to use the power of government to enact their priorities? 

I surely believe government has an important role to play in society - duh.  And I think that Christians should be engaged with government.  But I think we need to clearly articulate what we understand the role of government to be.  And I'm not there yet . . .

Perhaps I need a political science class to help me sort this out.