Why does evidence matter when the Bible is only a book of faith?

Is it "only" a book of faith?  What happens when the Bible is no longer a historically reliable account (in the parts that it claims to be)?

When you reduce these parts of the Bible down to a few general metaphorical ideas, you establish a way of interpreting scripture.  If you then apply that way of interpreting scripture in essential areas (like the historical crucifixion), you end up doing away with everything that matters about Christianity.  In short, you are calling the Bible a lie.  Joel S. Baden does this, I think without realising, in this article.

Let me make this really clear.  If you cast doubt upon one historical account, e.g. the waters parting for Israel, then you also cast doubt upon another, and Jesus no longer really rose again.

The apostle Paul has this to say about this situation:

"...if Christ has not been raised, your faith is futile and you are still in your sins..." 

- 1Corinthians 15:17