Paul Hiebert's 1978 paper 'Conversion, Culture and Cognitive Categories' poses the question of what's required to say someone is or isn't a Christian. He poses the senario of an illiterate peasant in Indian who professes faith after hearing the Christian gospel once. What would it take to say they're actually a Christian?
This sort of thinking could be applied to other things too - I'm a member of a running club, Suppose there's a person has paid up but never runs... and there's another person who runs with us but hasn't formally joined... who is the club member? So too, political parties etc.
Hiebert looks at the way Christian faith is popularly considered to be a bounded set - with a clear boundary between Christian and not a Christian based on orthodoxy or orthopraxy, where the key task is to get someone over the boundary. There's much good in the model, but Hiebert's question is - what about his new believer Papayya? He's in a culture without a church and he's just confessed Christ... his life looks fairly similar to before he believed. And if you quizzed him about his beliefs, so much of his thinking is shaped by his pre-Christian culture... he'd fail many tests of orthodoxy. Is he in, or out?
What if there's another model? Hiebert suggests centered sets. Here there is still a boundary but it's a centre point, Christ. What counts here isn't how close you are to the centre, but which way are you moving? One can be near or far from Christ in terms of knowledge or experience, the issue is whether one is seeking to follow Christ or moving away from him.
I've heard this choice described as the difference between having fences or gathering around a flag, well or campfire. Both still have a clear boundary category, both still have in/out criteria.
Fires, wells and flags are more attractive than fences, though both models still have boundaries in reality, and I'm not sure either can fully deal with the massive adjustments in worldview understanding that cause Hiebert to raise the question concerning new believer Papayya.
In the end, the Christian gospel is an in/out matter, Adam or Christ, lost or found. Both models accept that. Bounded-sets offer help when it comes to assurance - when you're in you're in, and nothing can take you out of Christ. Bounded sets offer helpful clarity and confidence. And fences protect those inside from wandering into danger, being attacked from the outside, and enable biblical measures of kind discipline that exclude to jolt someone into repentance. Bounded sets fit are institutionalised when a church has a formal membership, the approach enables strong mutual commitment. But, what do you then say or do about non-members...?
But Biblical language and categories also call for growth and progress,that the notion of centred set allows us to think more about what in-ness and out-ness look like, and offer the helpful categories of direction of travel, journey, L-plates, progress and joy in the faith that are helpful for aspects of Christian discipleship and soften the temptation towards them/us mentality. Campfires are attractive and warm and we - human beings - all need the gospel. Centred-sets remind us that there is more of Christ to be had for each of us. Papayya can be "in" because of his new direction of travel, though his faith is low on understanding and low on change. I something similar see that in the beginnings of my own walk with Jesus.
What if you think of a church in terms not of it's confessing membership but more in terms of its parish... everyone in the parish is either moving toward faith or away... on the final day, who is in and out will be evident. Here and now, many of our measures are what Jonathan Edwards calls 'signs of nothing' - no certain proof either way.
Healthy church practice surely needs to hold in tension the clarity of a bounded set and the movement of a centred set. Faith without boundaries is unkind. Faith without concern for growth is unclear.