Early Christianity is Catholicism! Therefore IT IS the only CHURCH!

For the first thousand years of Christianity there was no "Roman Catholicism" as we know it today, simply because there was no Eastern Orthodoxy or Protestantism to distinguish it. There was only the "one, holy, catholic church" affirmed by the early creeds, which was the body of Christian believers all over the world, united by common traditions, beliefs, church structure and worship (catholic simply means "universal"). Thus, throughout the Middle Ages, if you were a Christian, you belonged to the Catholic Church. Any Christianity other than the Catholic Church was a heresy, not a denomination.

-Religion Facts