Which church?..
There is in principle one Church, although there is a disunity between her bishops, and some diversity of the liturgy, so what we have is Catholic Churches in union with Rome, and various Orthodox Churches, and lesser known pre-Chalcedon Churches such as the Ethiopian Church or the Armenian Church.
As Catholics, we reject the Protestant concept of invisible Church of all Christian believers. When someone is validly baptized in a Protestant community of faith, he is still baptized with the one Catholic baptism, albeit he is not in full communion with the Church and is likely to fall away because of that.
Like I said, it is a complex subject, but I appreciate the questions.
We think there's only one.