I am concerned to explore the question how the mission of the Church is rooted in the gospel itself. There has been a long tradition which sees the mission of the Church primarily as obedience to a command. It has been customary to speak of 'the missionary mandate.' This way of putting the matter is certainly not without justification, and yet it seems to me that it misses the point. It tends to make mission a burden rather than a joy, to make it part of the law rather than part of the gospel. If one looks at the New Testament evidence one gets another impression.
Mission begins with a kind of explosion of joy. The news that the rejected and crucified Jesus is alive is something that cannot possibly be suppressed. It must be told. Who could be silent about such a fact? The mission of the Church in the pages of the New Testament is like the fallout from a vast explosion, a radioactive fallout which is not lethal but life-giving.
—- Lesslie Newbigin, The Gospel in a Pluralist Society
As I've said before, I agree with John Piper that "mission exists because worship does not," but I also believe that mission exists because worship does. When you're astonished by something, don't you want to tell somebody?