Thank you for your questions. I will happily take the first of these on now and try to circle back to the others at a later stage, if that is ok.
Using the Bible to prove the Bible
My first response to someone asking this question would be to probe the implicit hostility towards the Bible. Maybe with a question: what are the reasons that we ought to disregard the Bible itself as a source of evidence? Perhaps a follow-up challenge would include the question of whether the same strict criteria is applied to other books or not. For example, ought we to exclude Shakespeare’s works from the attempt to understand anything further about Shakespeare or Elizabethan society more broadly? On the one hand, it seems to me a strange standard to implement in general and, on the other, it wouldn’t make sense to apply this standard arbitrarily to the Bible, whilst not to other books.
The next thing to say: of course we need to go to the Bible to see if the Bible is trustworthy. Refer to my previous response for more on this (Ask Mike Day (March 18-22, 2019)), but suffice to say: if what we see in the Bible is internally coherent and corresponds to reality then it bolsters its case for authenticity.
Lastly, I do however understand the concern of ‘circular reasoning’ that may be in the questioner’s mind. So while we may go to the Bible to test consistency, coherence, correspondence, as well as pragmatic value, we may also go beyond the Bible. We do this to test its comparative accuracy with other historical texts and palaeontological, archaeological, sociological, architectural, and anthropological findings, amongst others. If the extrabiblical testimony accords with what is in the Bible, then the case is strengthened for the Bible’s reliability. Both internal evidence and external evidence is crucial for determining truthfulness.
I hope this helps a bit with your first question!