So, just what are we talking about?

[whyBish]

"The Bible contains metaphorical truths" is *not* an axiom.  It is an invitation to search the Bible for things that one believes, thus making those things (or, sometimes one's interpretations of those things) the axioms.  In many cases the axioms so generated are not used to develop any further viewpoints.  But, it is the possibility of generating so many axioms, and the fact that many of the axioms so generated can be contradictory, that gives rise to so many mutually antagonistic sects of Christianity.

It is possible to make from the Bible a set of self consistent axioms that can be the basis of an ethical life.

Anything logically derivable from the axioms is "true" within the system.  If that result is to be compared with something outside the system (i.e., if we are "modeling" something), then that result may be not "True" to the model.

If it is possible to both derive statement S and statement not S under the system, then the system is inconsistent.

Yeah, sorry, I rushed off to tennis after posting and then thought I should have mentioned internal consistency etc., although none of this was my point (I have no idea what my point actually was :P )

The only thing I don't get from your post however, is the first quoted paragraph.
How is that not an axiom? (Oh, and I did get the point about a system truth does not imply that the thing it modeled was True due to the modelling process)

One last note, many people can have belief sets that are internally inconsistent, and (dipping my foot into another sharkpool) Piaget believed that the realisation of these internal conflicts were a driver towards learning. I lived for about four years with a group of people that had the 'Literal' view of the Bible, but also (apart from evolution) did not want to contradict science. Suffice to say, there were many inconsistencies pointed out on both sides which lead to lots of thinking, which can only be a good thing. :)