Just for comparison, let's contrast the Catholic notion of church with prevailing notion expressed above, and that is that "church" is simply the body of all faithful believers in the Gospel. Let's see how that definition stands up.
Start by asking the question, "Where are they?" (these members of "the church") and what does this church look like? Can these members be found in a Baptist church? Maybe. Some of them. After all, "the church" is not a formal organization according to the definition under consideration. "The church" is just a collection of people with similar beliefs. Can members of the "true church" be found within a Lutheran congregation? Also maybe. How about Methodist? Maybe some of them are in God's true church too. Maybe there are even a few to be found in a Catholic parish community. And maybe some members of God's true church don't attend any formal organized gathering under any denomination. As long as they believe in the Gospel, they are members of "the church". That's what God's church looks like under the "nonRCC" definition of church.
With that understanding of what the church looks like and where its members may be found, let's see how "the church" today compares with the church as described in the New Testament. In your town, if you have a Baptist Church and a Lutheran Church, how often do you see those congregations worshipping together - even when their church buildings are on the same block? How often do you see a Lutheran pastor invited to deliver the sermon at a Baptist church, and vice versa? If you normally attend a Lutheran service, how comfortable would you be participating in the worship service at a Baptist church while on vacation in a strange city? Would you not rather search out a service at a church of your own denomination? You may be bound by a common belief, but you are not part of the same community of believers. Those not affiliated with any formal organization have it even worse, for where is their community? A common feature of the New Testament Church is that they gathered together for common worship. The sense of community was from the beginning an essential part of "the church". The abstract definition of "the church" as simply the set of people with similar beliefs lacks the component of community.
Now, to be sure, various specific denominations have very active community activities, with Sunday worship, Wednesday bible study, charitable group activities, Sunday School, Vacation Bible School, etc. Within their own denomination each named church recognizes the importance of community in the life of the church. That suggests that maybe one of them is "the church". Maybe the Lutheran Church, Missouri Synod is the one true church? I don't think even the Lutherans themselves claim that to be true. That still leaves us with a disconnected group of people defined only by the fact that they believe in the Gospel personally. And whatever Christian community they happen to be a part of has no regular connection with the larger church community. To be true to the Gospel, the church should be one, as Jesus prayed that they may all be one. Unity is another characteristic that was stressed in the New Testament. Paul warned against dividing into factions based on which preacher they happened to like (Paul, Apollos, Cephas).
In order to dismiss the Catholic Church as the one true church, one should be able to point a better alternative. And by "point to" I do not mean to simply give an abstract definition. The Catholic Church is criticized by pointing to specific people and actions and statements made by those people. And proposed alternative community should be just as visible in specific people. That I have not seen attempted here. All I have seen is a one-sided criticism of the Catholic Church without a specific alternative offered.
