Jim Wallis is often galvanizing public opinion, but I am sure that he regrets having done such an effective job of it this week. The decision to refuse airtime to an on-line ad from Believe Out advocating a welcoming posture toward LBGT adults and their children has precipitated a firestorm of criticism. And Wallis' effort to explain Sojourners' position has done little more than throw a damp rag on the conflagration.

The debate quickly became more than a debate over inclusion, however. It also became a debate over the viability of "Progressive Christianity" itself. Speaking for many, Jim Naughton, Canon for Communications and Advancement for the Episcopal Diocese of Washington wrote:

I was more or less in favor of the big-tent strategy pursued by progressive religious leaders in Washington in the wake of Barack Obama's election as president. The thinking—as I understood—went that in reaching out to moderate evangelicals on a certain set of issues it might be possible to make legislative progress on behalf of the poor. One upshot of that strategy was that Jim Wallis . . . became the embodiment of the Progressive Christianity in the eyes of the Obama administration and the Washington media . . . So here we sit, us religious lefties, with a movement led by a man who occupies a position to the right of Dick Cheney on LGBT issues. I am assuming people savvier and better connected than I am will understand that this situation is not tenable. The big tent collapsed this weekend, and it was Sojourners who yanked out the tent poles. Someone needs to alert official Washington that Jim Wallis and his minions no longer speak for us—if they ever did.

There is little to be accomplished by adding to the fire. So I won't break into the supply of well-cured wood behind the house. (It has been raining today and it's wet anyway.) But I have found myself wondering why the debate is about political agendas and the way in which the Progressive Christian voice is represented to the White House.

The answer, I think, is this: A debate is never over the issues it should be when the adjectives in a movement's label are more important than the nouns. Put another way: "Progressive" Christians have yet to articulate in theological categories what they believe in, so it is hard to identify what they believe out—except by resorting to political assumptions.

That's a problem for the movement and, if it isn't addressed, it will not last. Why?

Quite simply, the answer is this: If all that Progressive Christianity has going for it is that it is politically progressive, then there is really no reason to wrap churchy language around it. There's a political party for that. It is far better financed and organized. It's a bigger player than the church will ever be. And it doesn't need to worry about how it is represented to the White House. It can occupy it. Put another way: A religious movement shaped by a political agenda will never have significant traction, if it isn't fundamentally religious.

Of course, this is as true of conservative versions of Christianity as it is of progressive versions. And it raises serious questions about the perennial effort to rebrand the faith at all.

But be that as it may, the point is this: No expression of Christianity can give a convincing case for its existence without defining what it means to be a Christian. Without doing that, in fact, every debate like this will be more about politics and policy than about something spiritually definitive.

So, where does the conversation begin? With explicitly religious and spiritual questions, perhaps like these (though there is nothing fixed about the list):

Who is God?

Who is Jesus?

What is the reign of God?

What does life under the reign of God look like? How and where is it given expression?

What do human beings need from God?

What is the relationship between God and human beings meant to be?

What is the purpose of the church in giving expression to the reign of God?

How are those purposes realized?

What does the reign of God suggest about the membership, shape, and mission of the church?

I can't offer the answers to those questions. I am not even sure that it is important to institutionalize the "progressive" brand. Christianity, properly understood, has always struck me as a pretty progressive thing anyway and the noun has had more staying power than any of the adjectives. But in the absence of a conversation shaped by questions about the meaning and nature of our faith we will inevitably find ourselves talking about politics, the White House, and "wedge issues."

To "believe out" the church needs to know what it "believes in."