The Bible is a story. It is a story of God chastising, forming, and loving His family.
I cannot hope to understand a story if I deny the integrity of its characters. I can't claim that Hamlet in Act II is a different person than Hamlet in Act I and still hope to understand the story. I have no evidence that they're the same; I can't see Hamlet in front of me and must trust the author's honesty and the reliability of the other characters. To read Hamlet, I must make a leap of faith in Shakespeare, then see it bear out on the page. If, instead, I start reading with the certainty that it won't make sense to me, I will surely prove myself right.
Similarly, you cannot expect to understand the Bible if you read it without a faith in the story. The Bible is the instruction manual, not the sales pitch. To have an understanding of the Bible as a whole, you must start with a leap of faith - the same leap you give any book you read. To understand a history book, you must start with faith in the fundamental reliability of the sources and the intent of the author. To understand a novel, you need faith that the author intends to tell a consistent, understandable story.
Consider the Gospels, in particular. Within the Bible, the Gospels are messages of good news. Good news assumes both a preexisting belief in the source of the news and an acceptance of the bad thing the good news overturns.
I will not accept good news of a cure for my illness if I think that the letter is a forgery or fake, that the doctor is a quack, or that I am not sick. To appreciate and understand this good news, I must believe that the writer is trustworthy, the physician is capable, and that I am really sick.
To appreciate and understand the Gospel, then, you must already appreciate and understand the goodness and power of God, the honesty and inspiration of the evangelists, and your sinfulness.