Are there other models of spiritual life than the one described under sociological models? I think there are many, and I will present the second one here. First, I will describe the standard model.
Standard Model
The standard model I use for the dynamics of spiritual life is a single stock representing its value. This model is embedded within a full church growth model with enthusiasts and activists. I run the scale of the stock from zero, no spiritual life, to a maximum value given by Capacity of SL, figure 1. I chose to limit the scale because there is only so much life or activity a person can take in. We are finite beings, and it is likely that the properties of groups of people will also be finite. The closer life gets to capacity, the harder it becomes to increase further, balancing loop Bs1.
The driving force of spiritual life comes from activity in the church, usually from the active believers. If this force ceases, spiritual life will fade, loop Bs2. This loss represents the spiritual lethargy of individuals and groups. To maintain the church’s spiritual life, Christians need to do work. Hopefully, some of this will take place through the church’s regular preaching and worship. However, even that will depend on its spiritual content.
Multivariable Models of Spiritual Life
Spiritual life is a soft variable and challenging to quantify. A mathematical model is only an approximate representation of the real world. What if spiritual life were more complex than a single variable? For example, there is a type of life in the church that accumulates slowly through the regular work of active members in church activities, such as prayer, Bible teaching and worship. I am thinking here of activities with a spiritual component. However, even running a foodbank could count if it becomes a place where spiritual encounters occur.
By contrast, there are other ways spiritual life may increase and do so much faster. I am thinking here of the type of work that happens in revival, such as people being filled with the Spirit. It could be a prayer meeting where everyone is transported into God’s presence. The dynamical parameters of this immediate form of spiritual life will differ from those of the more persistent form described in the previous paragraph. For example, the persistent form may decay more slowly than the immediate form because regular activities generate it. Thus, its loss would be smaller.
An Example from Media
Some years ago, I modelled the news media response to political events and its effects on political party growth and decline. It struck me that the news media responded to different events in different ways. There were sudden events, such as a natural disaster. Typically, the media would be filled with reports for a couple of days, and it would be the lead article. However, if the situation did not change substantially, the event would quickly disappear from the news or rank very low.
However, the media also report ongoing events, such as politicians whose behaviour is suspect. Here, the media have an interest in keeping the story alive and often look for daily news to feed their story. Media reports generally persist for longer periods, even though they may not make headlines on every day.
I can apply the same thinking of models of spiritual life and investigate the combination of fast and slow changes in that life.
Stock-Flow Model
The model now needs two stocks. I will use the same basic outline as in Figure 1. I have called them Spiritual Life Immediate, indicated by SLi, and Spiritual Life Persistent, indicated by SLp, Figure 2. Notice that there is an extra loop in the persistent model, Rsp1. This loop is reinforcing and slows the build-up of the stock if its values are small. That is, it takes time to build the life of the church if it starts from a low spiritual base. By contrast, if there is a higher spiritual value, this loop helps drive the life’s growth. More life gives more life.
One result of the additional reinforcing loop is that persistent spiritual life must start at a nonzero value, since the increase in life is proportional to its value. I see this as capturing the fact that active believers must always have some spiritual life because they are believers. Although inactive believers will also have some spiritual life, they are not doing anything with it. It is not that they are completely lifeless; they are just inactive.
For spiritual life to influence conversion, combining the two forms of life together for a single output is easier. This may be done in various ways (see Hayward (2014) et al.). Here, I take the average of the two forms of Spiritual Life, which may be weighted to capture situations where the balance between the persistent (SLp) and immediate (Sli) forms varies. Thus
SL = w X SLi + (1-w) X SLp
where w is the weight.
Results
Figure 3 shows the behaviour of spiritual life. The persistent version is built slowly, and the immediate version is faster. However, in the long run, the persistent version is the more powerful. Note the slow rise of persistent life (red dashed curve). Although the increase in immediate life is faster (blue curve), its impact on the overall spiritual life is smaller (black dotted curve). Immediate life does not rise much after 10 years, but the overall life growth rate increases around 40 years due to the effects of persistent life.
The scenario I have in mind in Figure 3 is a church that begins with a very low level of spiritual life. Its active believers receive a sudden baptism with the Spirit, and a renewal movement begins in the church. The activists adjust the church programme to foster spiritual life among new converts. Although the immediate works of the Spirit are not neglected, the long-term effects of a church that is now more spiritually oriented become more prominent. The church of Pentecost transitions to the church of mission – the latter chapters of Acts!
In this scenario, the church takes a long time to grow (Figure 4), reflecting the time required for spiritual life to increase sufficiently (Figure 3). The immediate form of spiritual life would not be sufficient to cause church growth. The slower, persistent form is essential. Activists start by falling before they rise (Figure 4, red dashed curve). The effects of spiritual life take time to produce fruit.
Overshoot
By 100 years, the fraction of the church has fallen (see figure 4, red dashed curve). Higher growth has led to a weaker church. This decline should be a red flag for a future decline in church numbers. In fact, church numbers oscillate over a long period, figure 5. The oscillations are a demographic effect due to shifts among the different types of believers, compounded by the delay between the causes and effects of spiritual life.
These system effects may help explain the ebb and flow of churches over many hundreds of years. However, they do not completely explain the repeated revivals in, for example, Wales. There were at least 16 revivals during the 18th and 19th centuries. Some of these were sudden with no obvious internal cause. Rather, they were direct acts by God.
In some scenarios, the overshoot can lead to collapse. I think this mechanism can explain the rise and fall of historic denominations in countries like the UK and the USA. For well over a hundred years, they have been living on the fruits of earlier revivals and now face extinction as revival is no longer sought.
Missing Features
The model lacks important features. I would like to add renewal, where the work of the Holy Spirit may make inactive believers spiritually active. Further, renewal would also make active believers enthusiasts, figure 6. See the basic Renewal Model. Additionally, a spiritually active church may attract people because of its presence in a community rather than through person-to-person contact. My initial work in this area shows that these effects may reduce the severity of the overshoot.
I could produce other models of spiritual life, but I would have to be convinced that they add something to understanding church dynamics.