Because:
The most expansive and effective church planting movements grow by mobilizing the indigenous church to evangelize their community and region, and by equipping national church planters and pastors to faithfully teach God’s Word and to lead the local church into spiritual maturity.
Therefore:
The main role of an ex-patriot missionary is to work with local churches to equip and mobilize evangelists and church planters to go into unreached, unengaged, unchurched regions.
Even among the least reached people groups with only a few churches, indigenous leaders and their young churches are able to broadly and courageously proclaim the Gospel and plant new fellowships.