I'm understandably loath to address this issue as regards any Holy Books but my own, but the authors and early readers of the Bible
(and by "early readers" I mean practically everyone up until, say, the seventeenth century) operated under the assumption that God
did indeed exist
. There was no need to prove
it within its pages -- this was generally accepted as a fact of existence.
What the Bible tells us are things about God. What is He like? What has He done? What is our proper relationship to Him? Though you find plenty of smirking Greeks in its pages, lounging around the public squares and making fun of the Apostles, the arguments are all about these things. There are heathens aplenty, but no atheists, not yet. Flip back a little further and you'll see the same sorts of debates occurring between Jesus and the Pharisees and scribes.
The victories won in these arguments generally came not through methodical reasoning after the manner of the philosophers (you'll find plenty of reasoning in the letters of Paul, but he is speaking to Christians), but from the authority with which these men and women spoke. Those who heard them and joined their movement did so because it was clear to them that these people were on a Mission from God. They heard the word, and they believed.
And so it is today; in the Bible we have the testimony of some of our fellow human beings that at several points in human history, God intervened; and at one moment in particular, He won for us a staggering victory against evil and death and opened a way for us to be heirs to the Kingdom. That's the word, the only word we have to tell you, and its formulation over the millennia is, we believe, God's own attempt to tell you all these things.
We are obliged to relate this news to you in the best and most faithful way we can. We are not, however, obliged to make you believe it. The issue then is, do you hear authority in these words? When Jesus says that in God's kingdom "The last shall be first, and the first last," does this strike you as a statement made by someone who knows what he's talking about? Paul's declaration that "There is neither Jew nor Greek, slave nor free, male and female in Christ Jesus" -- is this Paul the ex-Pharisee, now tentmaker talking, or do these words come from a higher source?
In my own case, ideas like these troubled me for a long time; they leapt off the page and seized hold of me in a way I could not deny, though much of what was said frightened and angered me. In the end their power compelled me to set foot on the path and start looking for answers to my questions and doubts, because they were words I could never fully reject or ignore.
In a way this inability to shed ourselves of these ridiculous ideas (why shouldn't the first be first? What have the last done that deserves rewarding?) is true of our culture as a whole. The ideas I mentioned above and others like them served as the foundation of the abolitionist movement, the women's rights movement, the civil rights movement, and various land reform movements. Though the religious beliefs of the founders of my country are debatable, the Judeo-Christian idea that we are all equal in the eyes of the creator of the universe underlay much of their thought and in the end made us a lot more equal under the law than even they intended.
But this is of course not a logical argument. I am not saying that because I believe in the authority of the Bible as God's word and some other people who did some neat stuff did too, that you must do so as well. I guess what I am asking is that you consider not reading it, but hearing it. The authors are human beings like yourself, and they have seen something they must tell you about, something that has amazed them. Make it not so much a matter of you versus the Bible, or you versus Christianity. Listen. Try to make some human connection across the span of years. Then decide whether you believe that these are the words of madmen, fools, and liars.