Talking with my wife yesterday, in response to a non-Christian friend's abandonment of hope of getting answers on umpteen questions from the Bible, we talked through this idea. And, because I'm a read/write orientated thinker, here are my thoughts:
Leading with your best foot forward
One of the ways Christians do a poor job of explaining their faith to people on the outside (and, let's be frank, there is a rather large gap between the outside and the inside in terms of the way people think and process), is the tendency to atomise answers and fail to provide a coherent account of the Christian Faith as a meta-narrative.
To illustrate the difference, consider a parent trying to explain to their child why they cannot at this particular time eat ice-cream. One response is simply to invoke parental fiat, "No, because I have said so". Alternatively, the parent can provide an account of why it's not appropriate for their child to be eating ice-cream. Now, granted a slightly older more rational child, it's the second account that, I would argue, is both more compelling and intellectually honest.
The bible deserves at least the same. You're free to disagree with a coherent, full-orbed reading of it, but most outsiders never get that far. They come to a collection of ancient translated documents, and read it fairly disjointedly, without any of the tools they should use or a decent account of how the whole might be read as an integrated story of God, his world, and his redemptive plan.
This is the great strength of "biblical theology". That we even needed to use the adjective there shows, I think, how great a problem has developed! But, an ability to read the bible as an integrated whole with a simple major thread, yet a diverse and complex set of nuances, is really important. It's important in Christians being honest and not simplistic about their own scriptures, It's important for outsiders, to at least be able to argue with Christianity as a whole worldview, a package deal.