What is missiology?
How much is 15%?
Consider this relatively conservative growth scenario: If even 15% of the members of a congregation of 400 meeting in a room that holds 500 bring one person to Christ every year, in two years members will no longer be able to bring any more of their friends to church.
And if a church is not growing by 15% every few years, that means that not even [15%] of its baptized members are bringing someone to Christ. Could any pastor who takes Jesus’ promises about the fruitfulness of his church seriously be satisfied with that (Luke 5:1-10; John 15:8)–and not hoping, and yearning, and planning, for more?
Can we set a quota for the work of the Spirit?
Even if you do manage to send out 10% of your members every year for the first few years, you will see a law of diminishing returns begin to kick in. The amount of believers ready to uproot their families and plant a new church will not remain constant at 10%. I’m not saying mathematically it couldn’t happen; I am saying that I am very familiar with the most mission-minded, mature, church-planting churches in the nation, and I have never seen an example of a church that could sustain that level of sending. The first year you harvest that zealous group–who are in a place for a new challenge and ready to go with your new plant. The next year, you convince a few more, as people in your church are maturing and becoming more willing to sacrifice… but it probably will not be quite as many. Soon, you will have run the metal detector over the sand so many times that there just is not enough metal shavings left to send out in a new plant. And, even if you could maintain the 10% sending rate, you would not be keeping up with the conservative growth rate of 15%–which I still think is a low growth percentage in light of Jesus’ extravagant promises about the fruitfulness of his church!