Axiomatic opinions

Gary Crampton:
"An important part of the Scripturalist worldview is the epistemological distinction between knowledge and opinion. Throughout the history of Western thought, philosophers such as Parmenides, Plato, and Aristotle, have correctly differentiated between these two. Augustine and Gordon Clark are just two examples of Christian philosophers who have done the same.(36) There is a difference between that which we “know” and that about which we may have opinions…To “opine” something is not to “know” it. Justified truth is found only in the Word of God.

And is the epistemological distinction between knowledge and opinion knowledge or opinion? Is that distinction itself an object of knowledge or opinion? Does a Scripturalist know there's such a distinction, or does he merely opine that there's such a distinction? 

What's noncircular justification for this distinction? How does the Scripturalist come to know or justifiably believe such a distinction exists in the first place? 

The Scripturalist begins with the presupposition that the Bible is the Word of God; this is axiomatic. He then deduces everything else from Scripture.

Aren't axioms unprovable postulates? So if the presupposition that Scripture is the word of God is merely axiomatic, then that axiom would seem to be a matter of opinion rather than knowledge. And if that's just an opinion, so is everything deduced from that opinion. At best, a valid deduction from an axiomatic opinion. 

Given that presupposition, you can deduce other truths, but by what noncircular argument does a Scripturalist establish the given?