Third Sunday of Easter
To discuss evangelism without an explicit ecclesiology is to reduce Christian proclamation to marketing tactics.
The bottom line of an "instrumental" ecclesiology is that whatever form "church" takes in a given culture is nothing more than the best means to a particular end. The problem with this is that if "the church" has a particular existance as an institution created and upheld by the Trinitarian God, there are bits of its "DNA" that we will lose if we can't find it in the goals we have constructed.
If celebration of the Eucharist a key component for the very being of the Church, but a particular congregation cannot see how it contributes to its goals for ministry or spiritual formation, they will drop it just because they don't "get it."
A church with an instrumental ecclesiology will engage in faithful, formative practices only insofar as its leadership can give rational account as to why those practices are "good ideas." There can be no such thing as taking anybody else's word for anything, and the Spirit can never offer the Church a provisional "just because."
Instead of being shaped by the Christian tradition, such a church will only be shaped by those bits of it that it has deliberately picked out and reshaped in terms of its own rationality.
That may or may not be a problem; I see at least two valid opposing arguments in such a discussion...