Although there's some debate on this point, the main theme of the Book of Job seems to be the age-old theological question of why, if there truly is a guiding force at work in the world, bad things happen to good people. Much of the Old Testament holds to the idea that good works and piousness are rewarded, while bad works and heresy are punished. But even back when the Bible was written, people would have realized that not all good and bad fortune can be so easily explained. Job is tested by being afflicted with physical pain and the loss of his wealth and children, and his friends insist he must have done something wrong, but Job's eventual conversation with God (who appears in a whirlwind or a cloud) gives the impression that mere humans can never really know why God deems it necessary for bad stuff to happen. Still, if you have faith, things will work out all right in the end. Sure, you'll lose your kids, but you'll end up with new and better ones! Okay, so that part probably wouldn't appear if a similar book were written nowadays, but the belief that there is some kind of reason for all the crap that occurs still holds true today. Even those of us who don't believe in gods tend to cling to the ideals of justice and compassion, even though those also don't always work out.
Job is said to have lived in the Land of Uz, which I believe is actually the name that the most recent Hebrew translations of the Oz books use for that fairyland. It's not entirely clear where Uz is, but evidence elsewhere in the Bible suggests that it might be a name for what would eventually become known as Edom and Idumea. Since there are no mentions in the book of the Jewish people or the nation of Israel, it's often regarded as taking place in the time of the patriarchs of Genesis. There's also a tradition that Job was Egyptian, and either a king or an advisor to one. And other local interpretations have placed Job and Uz closer to the interpreters' homes (funny, that). I think the chances are that Job was never intended to be a historical figure, but simply a character in a fable. As someone who likes verisimilitude in my fiction, however, I can appreciate the attempts to locate the setting of the book.
Finally, on an unrelated note, happy birthday to vilajunkie!