Eckhard Schnabel has helped clear the missional fog for me. He's done an outstanding job of unpacking the mission of Jesus and the early church. Followed up by another volume on Paul the Missionary. Here's how he defines mission from a thoroughly biblical framework.
The term “mission” or “missions,” refers to the activity of a community of faith that distinguishes itself from its environment in terms of both religious belief (theology) and social behavior (ethics), that is convinced of the truth of its faith, and that actively works to win other people to the content of faith and to the way of life of whose truth and necessity the members of that community are convinced.
So what does a missionary movement do?
- Missionaries communicate the good news of Jesus the Messiah and Savior to people who have not heard or accepted this news.
- Missionaries communicate a new way of life that replaces, at least partially, the behavioral patterns of the society in which the new believers have been converted.
- Missionaries integrate the new believers into a new community. The new converts become disciples.
Let's get even more specific:
Missionaries establish contact with non-Christians, they proclaim the news of Jesus the Messiah and Savior (proclamation, preaching, teaching, instruction), they lead people to faith in Jesus Christ (conversion, baptism), and they integrate the new believers into the local community of the followers of Jesus (Lord’s Supper, transformation of social and moral behavior, charity).
His study of NT mission is very thorough but worth the effort. I suggest starting with Paul the Missionary.