Spiritual life is that aspect of a church that represents the activity of a church that is spiritual in origin. It is a work of the Holy Spirit in believers that assists the church’s witness by making enthusiasts more effective at making new converts. The spiritual life in a congregation can be encouraged by the activities of believers as they work together. Not all believers contribute to the generation of spiritual life, but those who do are much wider than enthusiasts.
This model is a generalisation of the original Spiritual Life model, where enthusiasts alone generated spiritual life. In this revised model, the church is divided into enthusiasts, active believers (activists) and inactive believers. Active believers help generate spiritual life. The conversion potential of the enthusiasts is the direct beneficiary of that spiritual life. The more life, the more growth, hence more life.
Spiritual Life
As the number of active believers in a church grows, there becomes more scope for improving the church’s spiritual life. Such improvement may be seen by more prayer, a greater understanding of the pertinent truths of scripture, and boldness in sharing the message. One example can be seen in Acts 4:23-31 where persecuted believers pray and receive power from God.
After they prayed, the place where they were meeting was shaken. And they were all filled with the Holy Spirit and spoke the word of God boldly.
Acts 4:31
Of course, works of the Holy Spirit in believers are works of God, not man. How, then, can people’s activity encourage this life? It is easier to see the reverse that human activity can quench the Spirit and reduce His activity. Do not quench the Spirit (1 Thess 5:19). Not getting in God’s way can be seen as a positive act that encourages the work of the Holy Spirit.
All models are subject to the proviso that God continues to act in the same way. The same is true for generating spiritual life. If God continues to bless the activities of believers aimed at improving the church’s spiritual life, then that life will increase.
One example of such a work is unity. Disunity quenches the Spirit. Maintaining unity will thus encourage the work of the Spirit. If God continues to act in the same way, then unity would improve the church’s spiritual life. In turn, this will enhance the likelihood of conversion, again, if God continues to act in the same way.
System Dynamics Model
The full system hypothesis is that the church generates spiritual life, which in turn improves the conversions of the church, reinforcing loop, R1, figure 1. The figure shows the church embedded in a population module in a feedback loop with Spiritual Life, also in a module. The modular structure is used to defer the full technical details of the model.

Figure 2 outlines the church growth model in the population module, figure 1. Spiritual life influences the conversion rate into the church. Also, the combined strength of the active believers with the enthusiasts generates their spiritual life. Enthusiasts are also active believers who also recruit.

The full church growth model in the Population module is given by the limited enthusiasm model with activists. The advantage of the modular approach is that the church growth model can be extended further, e.g. the Demographics model, keeping the central Spiritual Life hypothesis intact.
Spiritual life is modelled on a scale of zero to one using a single soft variable, figure 3. Balancing loop Bs1 prevents the variable from exceeding its capacity of unity by making Spiritual Life harder to produce as it approaches capacity. If the church fails to produce spiritual life, perhaps due to insufficient enthusiasts, then the life naturally decays, loop Bs2. A church needs to actively maintain its spiritual life otherwise it will fall away.

Further details of the concept of spiritual life are discussed under the Limited Enthusiasm Model and the Further Model Details page.
Scope of Applicability
The model can be applied to an individual congregation of a national denomination. I also intend to use Spiritual Life in a more comprehensive model of the rise and spread of Christianity over many centuries and its competition with other religions and ideologies. This comprehensive model is a long-term modelling project that will require the addition of other features.
Results of the Spiritual Life Model
A church starts small with a low Spiritual life. Active believers have some ability to generate spiritual life, which starts growing immediately, figure 4, red dashed curve. Church growth does not explode until the spiritual life has reached a threshold, blue curve. The church’s subsequent fall and recovery results from movements between enthusiasts, activists and inactive believers. In a full demographic model, these changes would be fewer.

The results show that churches can grow through increasing their spiritual life. That life raises its reproduction potential, figure 5. The growing reproduction exceeds the revival threshold, bringing revival growth. As the number of potential converts falls, the revival threshold increases until it surpasses the reproduction potential and revival ends.

The standard limited enthusiasm model has a constant reproduction potential. The spiritual life model allows for that potential to vary. Although more significant growth is possible, there are scenarios where the church overshoots and collapses due to its failure to maintain spiritual life. This instability is a result of missing features, as outlined below.
Further Results of the Spiritual Life Model
- Spiritual Life and Church Growth. Increasing spiritual life accelerates church growth. Failure to maintain spiritual life can lead to extinction.
Missing Features
The Spiritual Life model is not intended to be a complete model. Other features are not for a comprehensive church growth model.
- Social capital. The ability of the church to build the church structures that enable spiritual relationships within the church and with the community. See Spiritual Life in Dynamic Modelling.
- Institutionalism. The large churches develop institutional structures that support their size and complexity but take resources away from the mission. The result slows the effects of revival growth and its spiritual life. See the Institutional Model.
- Concern. When the spiritual life of a church declines, some people become concerned and take action to improve the church’s life. Revivals often start with people concerned about the spiritual state of the church.
- Legitimacy. The extent to which wider society views the church as legitimate. If it does, people may become part of the church by attraction rather than contact with an enthusiast.
- Unity and Internal Cohesion. A church that lacks unity and internal cohesion will undermine its mission and quench its spiritual life.
- Culture. When a church is acceptable to its broader culture, people may become cultural Christians. That is, they accept the general principles of Christianity but without any commitment that leads to church attendance or conversion.
- Geographical Spread. The ability of the church to grow through planting churches in areas where there are no Christians.