Continuing on the subject of The Plateau. There will be a subset of people on the plateau who are functionally atheist. I don't mean that they aren't believers (although they may be), but that the gospel is currently making no discernable impact over their day to day lives. They don't think about it, don't pray and don't seek to bring God glory in the warp and weft of life. They compartmentalise "the Christian bit" into an hour on Sunday. Therefore their approach to life is functionally no different to a non-believer.
Of course this may have a massive impact on a church if functional non-believers are present in any number. Any church leader will be understandably reluctant to conclude that people in his congregation who market themselves as believers in reality don't live like it. Especially if those folk have a degree of influence in the church. It will be all too easy to brush it aside with "of course they are – they are in church every week" rather than to confront the unpleasant truth.
On a related note, the same can be true in Christian Unions. I had a very interesting meeting with some university students at a good-ranking institution little while ago. We talked about whether they approach their study with Christian assumptions. I wanted to know whether they often considered what God thinks about what they were studying. What came out (student workers take note) was that most of them clearly believed core Christian truths and approached life with a Christian worldview but couldn't explain why they believed what they believed. In fact they didn't come close to being able to do so. And hence they had no sense that what they believed was true for all. It was in the realm of personal private opinion or preference. Most couldn't see that believing in salvation in Jesus alone implicitly means that the worldview of their non-Christian friends is incorrect.
They too were functional atheists. In this case they enjoyed worship meetings and all the paraphernalia that goes with having a close Christian community. But they were resting very lightly upon the world around them because they simply couldn't see that what they believed was any more pertinent to life or their study than what anyone else believed. They were Christian relativists. Their Christianity amounted to having a comfortable club that insulated them from the world.
I have commented recently in a couple of situations that believers ought to be able to say why we believe what we believe. Or else we are simply living blindly with someone else doing the thinking for us. Only to have the idea dismissed as "you are just being too intellectual. You are making unreasonable assumption about how much the average person can grasp." Too intellectual I may be, but I contend that this sort of compartmentalisation and lack of desire to have belief that is on a firm footing is a feature of people who have remained on a comfortable plateau, unchallenged. In countries where persecution is rife and being a real believer is dangerous I have no doubt that the percentage of people who are happy to remain as functional atheists is much, much smaller (or nil) and that everyone will be able to say why they believe it. Their answers might be existential – "I met God" – rather than intellectual, but they will be able to answer.