You're an evangelical Christian. You've been attending a Southern Baptist church. You move to a new town. Do you:
(a) automatically find a local Southern Baptist church and join it, or
(b) try out a few different churches regardless of their denomination - or lack thereof - and find one that you think fits you?
In my experience, almost all evangelicals today choose option 'b'. Why? Because few evangelicals actually identify as Southern Baptist, or Methodist, or Presbyterian, etc. Most will only go as far as to say that they happen to be attending a Southern Baptist church (if they are aware of their church's denomination, and many are not, and don't care either). If they're more advanced theologically, they might say, for example, that they are 'Reformed' in their theology, which might somewhat limit their choice of denominations, but they are still usually uncommitted to any one denomination or organization.
Such people, I say, are in an ecclesial no-man's-land.
They ultimately exist no where. They are unconnected in a real, tangible sense. They are Christian islands which, granted, may choose to freely associate with other believers, but only as long as they find that it "works for them". At best, some evangelicals might be willing to stick it out with a congregation through a hard time. But at the end of the day, it's only because they choose to do so (or because they think God is calling them to for the time being), but not because they think that that particular congregation is where they must be in any absolute sense.
This is because, for most evangelicals, Christianity consists almost exclusively of one's own personal relationship with God. And the reason an evangelical goes to church is to be helped with his personal relationship with God. If an evangelical feels like a church is doing that (e.g. has music he "connects with" and regularly delivers inspiring, relevant sermons), he'll attend and perhaps get involved. If he tries out a church, and he doesn't like the music, doesn't feel inspired by the preaching, doesn't like the community, or thinks it's too big or too small, etc., he'll move on to somewhere else.
There are several problems with this. Here are two:
First, for such evangelicals, there is ultimately no real, tangible accountability. Any given church/denomination can only keep a person accountable, whether it be morally or theologically, as long as the person lets the church/denomination do so. If the person reaches a point where they can no longer swallow a particular church's teaching, they can simply leave and continue their personal relationship with God - which is all that they think really matters anyway - somewhere else. Thus, at the the end of the day, Christianity can be whatever one wants it to be (or however one happens to think God wants it to be for him). (But you object: "The Bible is my accountability!" My short response: Your interpretation of it might be, setting aside the question of which Bible.)
Second, and probably most important, God is saving a people. There is only one Bride of Christ (Eph 5). There is only one Body of Christ (1 Cor 12). There is only "one flock and one shepherd" (John 10.16). Scripture calls us to be "perfectly united in mind and thought" (1 Cor 1.10). And Jesus prayed that all of his followers would be one as He and the Father are one, so that "the world will know that you sent me and have loved them even as you have loved me." (John 17.23) God is looking to unify all people in Christ, not to have a bunch of otherwise unconnected followers.
Many evangelicals, I believe, would honestly respond: But what other option is there? No church is Christ's Church. This is the best anyone can do.
But what example do we find of the Church in the Acts of the Apostles? Do we find it legitimate for individual Christians to believe whatever they want to believe and associate and dissociate with the greater group as they please, an ecclesial free-for-all? No! We see an organization with authority from Jesus himself, led by the apostles and those to whom they have also passed on authority, tangibly in charge of all those who would claim faith in Jesus (see Acts 15; also, all of the NT letters). That authority has been passed on, in apostolic succession, to our present day, and has been preserved in the bishops, priests, and deacons of the Catholic Church.
Jesus founded a Church, and the gates of Hades have not overcome it (Matthew 16.17-20); it is still here for us today. Christ has kept his promise and has not abandoned us (Matthew 28.20).
You can escape ecclesial no-man's-land.
In the Catholic Church, there is a sure place to belong, a true home for us in the faith that does not stand or fall based on our preferences or whether we think it is giving us the church experience we are looking for, but rests firmly on the fact that it was founded, and is today shepherded, by Jesus Himself. And knowing that it is the true Church of God, with Christ as its head, we can submit ourselves and be truly molded, morally and theologically, into faithful members of the people of God.
19So then you are no longer strangers and aliens, but you are fellow citizens with the saints and members of the household of God, 20 built on the foundation of the apostles and prophets, Christ Jesus himself being the cornerstone, 21 in whom the whole structure, being joined together, grows into a holy temple in the Lord. 22In him you also are being built together into a dwelling place for God by the Spirit.