Limited Enthusiasm Models

Enthusiasts are the subset of the church who are active in the conversion of unbelievers. They are “infected” with religion and pass it on to their friends, family and contacts. The result is that religion spreads like a disease, and the church grows. Growth ceases because enthusiasts lose their infectious enthusiasm and are thus unable to convert people fast enough from the shrinking pool of unbelievers. These hypotheses can be expressed in the system dynamics diagram of the limited enthusiasm model:

limited enthusiasm model outline

There are three categories of people: unbelievers, enthusiasts (or active believers) and inactive believers. These correspond to the susceptible, infected and removed categories in the spread of an infectious disease.

In the basic model, new converts are the primary source of enthusiasts because they have the most contact with unbelievers. Extended models include births as a source of believers (Demographics Model), existing believers as a source of enthusiasts (Renewal Model), and the work of the Holy Spirit in conversion (Spiritual Life Model).

The Models

Limited Enthusiasm – Revival

Understanding the dynamics of revival by analogy with the spread of disease. Revival growth threshold – how a small number of enthusiasts can make a big difference.


Long-term Limited Enthusiasm model, including births, deaths and leavers. Extinction threshold and the survival of churches and denominations.

A version with only reversion is sometimes used for short-term data fitting.

Demographics flows


Growing the church by spiritually renewing its members. Enthusiasts are generated from existing inactive believers. Such renewal allows a critical mass of enthusiasts to initiate revival.

Revival Growth in limited enthusiasm model

Spiritual Life

Enthusiasts generate spiritual life in the church, which in turn makes them more effective in conversion. Spiritual life covers works that build people up in Christ, through the Holy Spirit, and glorify God.

Holy spirit window of St Mungo's Balerno


Membership figures are generally greater than attendance figures in declining churches. Vice versa in growing churches. How does this come about?


Inward migration can be a big help in growing a church. It can even tip a church into revival growth.