How so? You asked for the definition of the church that people here were talking about—and Mung gave you a standard definition which has been recognized by many millions of Christians for centuries. How is that “useless”?
I find it difficult to believe that you would not be at least generally familiar with the Westminster Confession of Faith. In any case, the answers to your questions are just a Google search away. Even before the Internet, nearly every secular encyclopedia included an article answering those questions.
Your questions are a bit like arguing with a competent dictionary over the meaning of a well understood word. Word definitions are a reflection of common usage. The “authority” of a dictionary’s definition of a word—if the lexicographers did their jobs well—is in reflecting the understanding of the majority of speakers who use that word.
This topic also brings to mind one of my pet peeves: the silly argument in the form of a question “Then who or what created God?” The standard definition of God includes non-creation, the always existing One. So even atheist philosophers have no problems using the standard definition of God, despite the fact that they don’t personally affirm that such a being exists. Words have meanings. To reject their standard meanings for no good reason simply takes one into futility and nonsense. It makes meaningful dialogue difficult.
My second peeve along that line is the childish insistence by some that they must always spell God in lower-case (“god”), as if that makes some sort of substantive protest. Regardless of whether one affirms the existence of God, proper nouns in English are capitalized. So even if I don’t believe Thor or Krishna exist as real beings doesn’t mean that it is anything but ridiculous for me to insist on spelling those names “thor” and “krishna.” Indeed, if I believe that Thor and Krishna don’t exist as real beings, what do I achieve by misspelling their names? I only display my ignorance of basic English that I was supposed to learn in elementary school. (The rejection of such a standard convention reminds me of similar attempts-at-insult tactics which Ken Ham et al use, such as inserting the words “so-called scientist” before the name of some famous scientist they don’t like. They apparently think that the subject’s earned Ph.D. in a scientific field and/or their peer-reviewed publications and important discoveries can be summarily dismissed simply by adding an insulting jab before their name. There is far too much childish nonsense of this sort in far too much of the propaganda coming from both sides of those atheist vs. theist debates. As I’ve said many times before, the two sides often fall into surprisingly similar silliness.)