Easy, it is implicit in Scripture, in which men discerned what is of God versus what is not, without an infallible magisterium. Do you deny that? Tell me how the Scriptures, by which substantiation the NT church established Truth claims upon, came to be established as authoritative Scripture.
And how come you did not answer my questions?
Because I have no interest in the magisterium. I asked a simple question in post 59. It is based on a snip from the OP. Of course, it is the acme of foolishness to try to discuss the content of the article that was posted.