In some ways, it is rather odd to start rethinking with the Church. After all, the Church is emphasized only in the New Testament (it is in the Hebrew Bible, but not in the same capacity) and only after the work of the Messiah brings the eschatological fulfillment of Israel's hopes to bear. History, however, has shown that the Church -- where Christians of all stripes live and move -- has not been particularly faithful to its mission or even to its constitution. From early on, it has been gnosticized and mysticized beyond any reasonable recognition of an institution that would have grown out of Temple and synagogue. However, this is where we most fully image the Messiah, as his body, so the Church is indeed one of the forgotten emphases of the faith, one that desparately needs to be recovered before any positive steps can be taken in the redemptive acts of God in the world.
Rather than talking about the marks of the "true" Church, which could be classified as one of the most damaging and violent debates of all human history, re-examining the difference between visible and invisible Church is in order. I am used, in the past, to speaking of the invisible Church as being those who "truly are in faith" as opposed from the "masses" who populate the pews. Philip J. Lee, in his wonderful Against the Protestant Gnostics, calls this what it is: gnostic elitism, leading to a bifurcated people of God, the superspiritual versus the moderate or the normal. Really, this gnostic belief is the same as the Judaizers, only in different terminology: you must be circumcised to be a part of the Messiah's people, or, you must have "true" faith to be part of the Church. Since we can never know for certain whether or not anyone other than ourselves have "true" faith, we must rely instead on the visible Church as our means of defining the community of God's people. In other words, as far as humans are concerned, those who are united with the Messiah are those who unite with his people in worship -- which seems to be Paul's argument throughout the book of I Corinthians. To take it a step further, though, the argument can (and should) be made that the only real example of what the Church is, is found in the local parish. The Church, the true Church, is made of a collection of real people in real places that have participation with the Messiah through faith and therefore have participation with each other, the Messiah's body. The word koinonia, which often is translated rather dully as "fellowship", has this double edge to it: we participate in the Messiah, so we participate with each other. The idea of the imago Dei finds its fullest expression here as well: if the Messiah is the imago, and we are united with the Messiah, even called by his name (12:12), then we -- as the body -- are imago Dei as well. (A quick note to say that this does not mean that either individuals or those outside of the Church are not imago Dei, but the Church qua Church is the expression of the renewed, redeemed imago found in the Messiah).
What then of the invisible Church? We do have the "wheat and tares", however I'm not sure if that parables applies outside on the historical division between those who are allegiant to the Messiah and those who are not, evidenced at AD 70 and AD 135. We do have a wonderful model to consider, though, in the book of Revelation. In God's throne room, where the seer John is taken up, we see not only the redeemed of Israel (the symbolic 144,000), but also ones from "every tribe, tongue, nation in the earth". While we normally experience the Church only on the local level of real people that we know and can interact with, when we worship the one true God, we join the rest of those who are outside of our parish community in heaven, so that the Messiah's body is one on the local level and one worldwide.
The question becomes, and quite relevant, what makes the Church itself? The word itself, ekklesia, comes from the idea of being "called out"; called away from being destructive and dehumanizing, called into a mission of living a truly human life in the midst of sin -- characterized by hospitality, mutual submission, and self-giving. In an earlier post I talked about the unfortunate marriage of religion and power, or probably better put, religion and violence. The New Testament is clear, it seems to me, that the Church is the court of the Messiah, his Session if you will: Paul says that those "called out" are "seated in the heavenlies with the Messiah" -- that seating, of course, is next to the one enthroned at the right hand of God the Father. However, that rule is not to be "live the Gentiles who lord it over their subjects" but rather "the greatest among you shall be the servant of all". The rule of the Messiah turns all other rule, by what Paul calls the "principalities and powers", on its head, openly shaming all those who call themselves the "true authority" or the "answer". The Church, the visible Church wherever it is, is supposed to lead this -- by leading lives characterized by love, mutual edification, and worship of the true God, who is the Creator and, through the Messiah, is the Redeemer of Jew and Gentile.