In response to Francisco's post, I think that it is important to remember that no culture is so far gone as to be unsalvageable. While I agree with his point about establishing small, intense communities as a basis for the faith to flourish, I also believe that it is important not to set ourselves in mortal combat with the culture in which we live. In fact, the result of these intense communities should not be a sort of insularity, but an openness to everything the culture gives us It is from the community that we gain the strength to test everything, retaining what is good (1. Thess 5:21). I'll come back to this point in a minute, but first I want to make a distinction.
H. Richard Neibuhr, in his book Christ and Culture, sets up several different models by which it is possible to conceive the relationship between his two subjects, three of which I think are particularly helpful: (1) Christ against culture; (2) Christ of culture; and (3) Christ transforming culture. The first is the mistake of seeing Christ in total opposition to culture. It leads to a sort of isolationism, a "Holy Huddle," in which Christians turn our back on everything the world gives us and create a sort of alternative subculture. The second sees the culture as Christ's manifestation of himself in the world, and, as a result, too quickly acquiesces to whatever interpretation of goodness the culture puts forward. But the third sees Christ seeking to remake the culture, to seize on what is good in the culture and multiply it, while decreasing what is evil. This third one, I think, is the most challenging to us as Christians - we get neither the pleasure of total rebellion nor the comforts of acquiescence - but it is also the most authentic response to Christ's presence in our lives.
It is from this basis that I think we Christians have a obligation to genuinely engage the culture, and seek instances of goodness. And again, this cannot occur outside of the context of some kind of true community; without community we'll have neither the strength nor the wisdom to properly engage it. But from these communities, we have to reach out to the culture and seek its transformation, rather than simply live apart from it. We take our model from Christ, who came into the world in order to make it whole.
This plays itself out in all kinds of ways, but I'm now going to try to make this concrete by focusing on the example the arts. Many Christians seem to believe that the relative worth of a work (a film, a song, a book, a painting, anything) is inversely related to the amount of sexual, profane, or violent content it contains. However, I think the gift of community enables us (and the calling of Christ draws us) to seek what is good in a film that may contain a foul language or a sexually explicit scene (of course, I understand that this calling is tempered by the extent to which is causes any one of us to sin). And it may be that it says something true, about longing, desire, love, forgiveness, humanity, or even faith incredibly powerfully. And yet a "Christ against culture" mentality asks us to reject the piece wholesale, rather than embracing the beautiful invocation of truth rendered by the artist.
Our faith is in He who makes all things new. I think that these small communities provide a necessary component to being able to live as though that fact is true. But we have to remember that He can (and in important ways, does) transform the broader culture.