You’ve no doubt heard a proposition like one of the following:
“If each Christian won one more person each year…”
“If the church doubled in size each year…”
Or, my personal creation: if 1 person discipled 10, who each discipled 10…
1x10x10x10x10x10 = 100,000 discipled.
Of course, this rarely happens. Why not?
We can blame it on apathy; or, as Zwemer did, on the ‘wicked selfishness of Christians.’ I theorize the real reason is a little more dull, and has to do with “Dunbar’s Number,” uncovered by the psychologist Robin Dunbar. This is a theoretical mental limit on the number of people—about 150— with whom you can have a ‘stable’ social relationship.
There have been a variety of reasons suggested for why this is the case: Dunbar extrapolated it from studies of primates and correlations in brain sizes. Whether you blame it on the size of your head or the amount of time you have to spend with people (vs. work, sleep, family relationships, etc), the obvious reality is: you can only be “besties” with so many people.
Further: ‘Dunbar’s number’ is actually a series of numbers. ‘150’ are ‘casual friends’ who you might invite to a large group event. Closer to you are the ‘50’: you see them often, might have some of them over for dinner, but are not ‘best friends.’ The ‘15’: who you turn to for sympathy, confide in, seek help from. Finally, the ‘5’: close supporters, intimates, often family members. (And, more broadly: ‘500’ acquaintances, and the ‘1,500’ is your wider ‘tribe,’ for whom you can probably put a name to a face.)
If you’re going to evangelize someone (‘go over and share the Gospel with them’), they are probably somewhere between your ‘500’ and your ‘50’. But if you’re going to disciple someone—spend time with them on a semi-weekly basis, probably—they will rapidly become at least one of your ‘50’ if not one of your ‘15’.
And there is one of the costs. Ask yourself: how many people do I have regular, close, weekly, semi-daily or daily contact with? Make a list. Several names are probably family (I have a wife and four children on my daily list). There are people we work with, people we go to church with, who we hang out with, and so on.
What you will probably see: of the 5, 15, and 50 slots you have, most are already taken up by believers. One reason: most Christians live in places where Christians are the vast majority (so most of the people you naturally know are believers). Second: most Christians were born into Christian households and grew up as Christians, so most of your ‘5’ and ‘15’ were Christians before you arrived. Third: in our regular social contacts, we prefer people like us (‘don’t smoke, chew, or run with those who do.’)
Discipling someone requires spending time with them. But if it means one of our ‘150’ becomes one of our ‘50,’ it also means we will (probably) spend less time with someone else—one of our ‘50’ will become one of our ‘150.’ We only have so much time.
Of course, maybe you already have a non-believer in your ‘50’ or ‘15’. Why not disciple them? Here’s the second issue of Dunbar’s Number for us: we can offer them the Gospel, but the challenge is their ‘5’, ‘15’ and ‘50’.
In The rise of Christianity, Rodney Stark details how the sociological process of conversion makes it more likely when “people have or develop stronger attachments to members of the [Christian] group than they have to nonmembers” (p. 18). The nonbelievers we meet will likely fall into one of three categories: