John 15:5 "I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing."
Most missionaries present the same goal to their mission board: church planting. They will either start or serve in new churches. And church planting is an effective long-term means of establishing Christianity in an area. The problem is, it rarely works. Almost all new churches fail. In fact, the most successful means of starting new churches, by far, is to have a church split.
Starting a new church is extremely difficult, and the failure rate is extremely high. Different groups use different methods, and most of them don't work. In other words, God doesn't often call Christians to plant churches, but that's what missionaries try to do.