In chapter twelve of David Bosch’s “Transforming Mission” he discusses the historical shifts in Protestant thinking regarding the relationship between church and mission.
To fully understand these shifts Bosch argues one must consider the contributions made by the world missionary conferences from Edinburgh (1910) to Mexico City (1963).
When discussing the Willingen conference (1952) Bosch writes:
Willingen began to flesh out a new model. It recognized that the church could be neither the starting point nor the goal of mission. God’s salvific work precedes both church and mission. We should not subordinate mission to the church nor the church to mission; both should, rather, be taken up into the missio Dei, which now became the overarching concept. The missio Dei institutes the missiones ecclesiae. The church changes from being the sender to being the one sent.
In a pamphlet published [after the conference], Newbigin summarized the consensus that had by now been reached:
(1) “the church is the mission,” which means that it is illegitimate to talk about the one without the same time talking about the other; (2) “the home base is everywhere,” which means that every Christian community is in a missionary situation; and (3) “mission in partnership,” which means the end of every form of guardianship of one church over another.