Question: "What does the Bible say about church growth?"
Although the Bible does not specifically address church growth, the principle of church growth is the understanding that Jesus said, “I will build my church, and the gates of Hades will not overcome it” (Matthew 16:18). Paul confirmed that the church has its foundation in Jesus Christ (1 Corinthians 3:11). Jesus Christ is also the head of the church (Ephesians 1:18-23) and the church’s life (John 10:10). Having said that, it should be remembered that “growth” can be a relative term. There are different kinds of growth, some of which have nothing to do with numbers.
A church can be alive and growing even though the number of members/attendees is not changing. If those in the church are growing in the grace and knowledge of the Lord Jesus, submitting to His will for their lives, both individually and corporately, that is a church that is experiencing true growth. At the same time, a church can be adding to its rolls weekly, have huge numbers, and still be spiritually stagnant.
Growth of any kind follows a typical pattern. As with a growing organism, the local church has those who plant the seed (evangelists), those who water the seed (pastor/teachers), and others who use their spiritual gifts for the growth of those in the local church. But note that it is God who gives the increase (1 Corinthians 3:7). Those who plant and those who water will each receive their own reward according to their labor (1 Corinthians 3:8).
There has to be a balance between planting and watering for a local church to grow, which means that in a healthy church each person must know what his/her spiritual gift is so that he/she can function within in the body of Christ. If the planting and watering get out of balance, the church will not prosper as God intended. Of course, there has to be daily dependence upon and obedience to the Holy Spirit so His power can be released in those who plant and water in order for God's increase to come.
Finally, the description of a living and growing church is found in Acts 2:42-47 where the believers “devoted themselves to the apostles' teaching and to the fellowship, to the breaking of bread and to prayer.” They were serving one another and reaching out to those who needed to know the Lord, for the Lord “added to their number daily those who were being saved.” When these things are present, the church will experience spiritual growth, whether or not there is numerical increase.