THIS IS A MUST-READ BOOK. Go buy it, and read it two or three times. Now. Get to it!
We should all be thankful to Flett for publishing this volume with Eerdmans, for it is accessibly priced. You therefore have no excuse for failing to buy (and, consequently, read) it. In any case, here is a juicy tidbit to wet your whistles.
John G. Flett, The Witness of God: The Trinity, Missio Dei, Karl Barth, and the Nature of Christian Community (Grand Rapids, MI: William B. Eerdmans Publishing Company, 2010): 9-10.
Both the decisive force and fatal flaw of missio Dei rests in its relationship to the doctrine of the Trinity. As propounded to date, the concept is deficiently Trinitarian, and the wide range of its contemporary problems is a direct result of this single lack. Reference to the Trinity distanced mission from every particular human act, but, as now a divine attribute, uncertainty arose over the practical transition from divine being to the human missionary act. Missio Dei’s vacuity emerges at this precise point. Material formulations of God’s connection with the world was reduced to the language of “sending,” with the effect that his “sending” being included more the particular sendings of the Son and Spirit. Missio Dei provides a Trinitarian illusion behind which all manner of non-Trinitarian mediations operate with sanctioned impunity. The Trinitarian formula is pure preamble. This explains how a wide variety of seemingly incongruous positions can all lay claim to the name missio Dei.