Willimon gave a pretty clear explanation of the "cultural battle" we really face

Sometimes in leaning over to speak to the modern world, I fear that we may have fallen in! When, in our sermons, we sought to use our sermons to build a bridge from the old world of the Bible to the new modern world, the traffic was only moving in one direction on that interpretive bridge. It was always the modern world rummaging about in Scripture, saying things like "This relates to me," or, "I’m sorry, this is really impractical," or, "I really can’t make sense out of that." It was always the modern world telling the Bible what’s what.
I don’t believe that the Bible wants to "speak to the modern world." Rather, I think the Bible wants to change, convert the modern world.

A Peculiar Prophet: On NOT Reaching Our Culture Through Our Preaching

The image of "falling in" is a good one.  This is what I fear sometimes when Progressive groups talk more  about what "America" means than they do about the nature and purpose of the church.  It seems that in seeking to "be relevant" and "use a language we can all understand",  we end up understanding the church more like a modern nation than an ecclesia. I found a refreshing angle on this also in Larry’s post yesterday