When we use the term "mission," what kinds of things can we be referring to? People who "Go on missions" or who "do mission" often are doing one of the following. I think it's helpful to have some broad categories: 1. Serving the local church. Typically short term or recurring short term trips of service to the Christian community,things like medical trips, children's ministry, building construction, legal or financial services, vocational training, etc.
2. Serving the local (Christian+secular) community. Some variant of the first option aimed at the broader community, often as a stepping stone to enabling the local church to witness etc.
3. Witness. Some variations of short or long term enable the individual to be a witness in a secular context: eg tent,among, business investment, teaching, sports ministries, etc. Here I am thinking of people who do not go necessarily to evangelize, but rather to be a witness through the demonstration of the Christian life lived.
4. Evangelism. This is perhaps what we most often think of in terms of mission: overtly sharing the gospel across languages and cultures. Forms can range from door to door sharing, House to house, literature distribution, film teams, dramas, large or mass crusades, evangelistic concerts, etc. The key here is the sharing of the gospel with the intent to make converts who are usually funneled toward churches. Billy Graham was an evangelist. Unfortunately evangelism that does not yield or is not service to stages 5-8 will often be unharvested fruit. We must be careful of flinging seed without a thought for harvesting.
5. Disciple making. This is a next step beyond the first step of evangelism and profession of faith. Disciple making is a longer term relationship of spiritual mentoring and accountability. In my view this cannot be done in the context of a single short term trip, and it's hard to do with recurring. It requires language and culture acquisition. It is most effectively and efficiently done in the same culture context but for the gospel to spread it must sometimes be done cross-culturally.
6. Church gathering/planting/pastoring. As disciples are made and gathered, church structures of some kind must be developed. This is another area where missionaries can help, though we must caution is a high risk endeavor. Culture creep can happen at the evangelism and disciplemaking stages but I think nowhere is it more possible or dangerous than here. Whereas broad cultural imports often neuter evangelism, a small amount of bad culture can cross through high trust channels at the church planting stage, get translated into a different culture and go on to infect the church structures that are reproduced. Culture at the evangelism level often yields spiritual sterility; imported culture at the church level can spark metastasizing cancers. Nevertheless when missionaries serve the local church by helping them develop accountability to biblical patterns, strong healthy systems can thrive.
7. Reproducing and multiplication. Missionaries are most effective when they help new church networks etc become rapidly multiplying movements. This requires encouraging simplicity, accountability to scripture, and wide implementation of disciplemaking not just by "professional clergy" but lay believers too. Catalyzing movements is how we "move the needle."
8. Movements birthing movements. The most effective movement starters are existing movements that know how to implement these 7 stages. Missionaries who help movements jump the cultural barrier into nearby peoples can help birth astronomical change.
Note that as missionaries move into 6-8 above, ironically, their efforts will be increasingly questioned by other missionaries who are more used to/comfortable with areas 1-5 and some 6.