Results of the Variable Demand Model
Reversion is the acting of leaving the church; people reverting from faith back to unbelief. Even if there are no limits to growth on the joining process, if people leave the church, then its growth will be limited by the leaving rate. If those who leave are hardened before being open to rejoining, the growth is further limited.
Reversion Limits Church Growth
Consider a church with a joining rate of 4% and leaving rate of 2%. Let it start small, in a population of 10,000 people where everyone is open to joining the church. Despite the higher joining rate, the church fails to attract all the population, figure 1.
Although the church has rapid growth for 30 years, it peaks and falls back slightly to less than half the population. With a softening rate of 3%, the stable number of open unbelievers is higher than the hardened. Nevertheless, both persist.
Higher Leaving Rate, Smaller Church
If the leaving rate is higher, the limit to growth is lower. Although this result is “common sense”, sometimes people think leaving rates do not matter as long as people keep joining the church. Using the same joining and softening rates as figure1, figure 2 compares the effects of leaving rates of 2%, 3%, 4% and 5%. There is a large drop in the stable level of the church between 2% and 3%. The leaving rate is very sensitive to changes when small. Churches with a low leaving rate should be particularly careful to prevent the rate growing as more reversion will seriously affect their prospects for growth
Hardening of Unbelievers Limits Church Growth
Let the reversion rate (4%) be higher than the joining rate (2%). Figure 3 compares church growth for four different softening rates: 1%, 3%, 6% and 10%. For the lowest softening rate, the stable church has the smallest numbers. There is a marked overshoot, caused by the long delay before hardened unbelievers become open. For higher softening rates, the overshoot is less pronounced, and the church reaches a higher limit.
Strategies to Raise Limit to Growth
There are clear policy decisions to help churches raise limits to their growth. Firstly, they should work hard to avoid people unnecessarily leaving the church, perhaps through better pastoral care keeping open relationships. Secondly, if people do leave, the church should try to maintain friendly contact so that they remain open to rejoining the church. Both these strategies are particularly important for the children of existing members who can easily drift away from a church. Good young people’s work is essential.