A little detour on Barth...
Last century, Karl Barth was key in re-emphasizing mission as the outflow of the life of God. At the Brandenburg Missionary Conference in 1932 he said:
"Must not even the most faithful missionary, the most convinced friend of missions, have reason to reflect that the term missio was in the ancient Church an expression of the doctrine of the Trinity-namely the expression of the divine sending forth of self, the sending of the Son and Holy Spirit to the world? Can we indeed claim that we do it any other way?"
The mission of God flows from Father to Son to church and out to the world. And just as the God from whom this mission flows is a Gospel God - One who is who we see in the events of the gospel - so His mission is a gospel mission. Just as the Father committed His words (remata) to the Son (John 14:24), the Son entrusts them to His followers (John 17:10) to be taken out into the world (John 21:20).
For this reason Barth was very particular about what he thought mission to be. It is a word-y business. It is about proclamation, about publishing this Gospel to the world. Consider these quotes from a variety of his writings:
“The essence of the Church is proclamation.” (Homiletics, p40)
“the event of real proclamation is the life-function of the Church which conditions all the rest.” (I/1,p98)
“The first if not the only thing in its witness is the ministry of the viva vox Evangelii to be discharged voce humana in human words. It is its declaration, explanation and evangelical address with the lips.” (IV/3, p864)
“…we learn from the Biblical witness to revelation that, over and above the command to believe, love and hope, and distinct from the command to call in common upon His name, to help the brethren, etc., Jesus Christ has given His Church the commission to proclaim, and to proclaim through preaching and sacrament.” (I/1, p62)
“At bottom, the Church is in the world only with a book in its hands. We have no other possibility to bear witness except to explain this book.” (God in Action, p107-108)
Now, before we ever write off such a mission as narrow - ignoring the social and political needs of the day - consider article 6 of the Barmen Declaration which Barth penned in Germany in 1934:
“The Church's commission, which is the foundation of its freedom, consists in this: in Christ's stead, and so in the service of his own Word and work, to deliver to all people, through preaching and sacrament, the message of the free grace of God.”
Consider the context. Germany. 1934. Wouldn't there have been immense pressure to deliver another message alongside that of the 'free grace of God'?? Wouldn't we have been tempted also to address the extemely pressing social and political needs of the day??
Yet Barth's definition of mission speaks extremely pointedly into the social and political needs of the day because it refuses to deal with those needs on their own terms. Instead, the church serves and confronts the world (even Nazi Germany!) by first serving its Lord. This service is gospel proclamation. And through it, the world is confronted with its true Fuhrer (Christ) and its true Reich (the Kingdom). The church most engages the world when it most rejects the world's agendas and presses its own - the Gospel of Christ.
For more on this see my essay on What is the mission of the church?