I've often wondered if much of the confusion in Lutheran ecclesiology is due to the fact that we tend to identify two distinct but related entities: the Kingdom and the Church.
The Kingdom is by its very nature "invisible" - "within you" as our Lord put it, or "righteousness, peace, and joy in the Holy Ghost" as St. Paul expressed it. In "this world" it is not seen, but consists in the union accomplished in faith between persons and the Blessed Trinity.
The Church is by its very nature "visible" - that is, it is the manifestation and sign of the Kingdom in this world. Schmemann once said it like this, I think, "the Church is the sacrament of the Kingdom for the world." The Church is the "x marks the spot" of the Kingdom in this world. Find her and you'll find an entry point into the invisible Kingdom of God.