We are not omniscient. God (if he exists) is omniscient. Therefore by definition we would be lacking information since our knowledge is only a subset of all knowledge.
Why is god omniscient if he exists? That is a rather large assumption. In fact, I would suggest that notions such as omniscient and omnipotent are really impossible and nothing but hyperbole. You can have neither an unstoppable force nor an immovable object.
But still, where do you get that god is omniscient? Has he guessed a long secret number you had in your head? Is there a verified, recorded incidence of him demonstrating what could only be the result of omniscience?
I think you probably meant the jewish god yahweh is omniscient according to the stories that describe him ... even though the stories were adaptations of earlier stories.
You see this is the problem I have - you want to believe in a god where the only 'evidence' you have is some old story book ... but we do have evidence that those stories were simply copies and adaptations of other stories which describe different gods.
Here's one for you:
"I'm awesome, super kind, generous, I know everything, I can do anything. Anything I do is good, even if you think it's crappy - you just don't understand."
Now, using only that description can you prove or disprove ANYTHING about me? (discounting anything else I say - for this illustration I never say anything else). Oh, and no one has ever met me or met anyone who met anyone who met me. And no one has ever heard me, or seen me do anything ... in fact, it's an anonymous internet account that posted the message.
Trying to base anything on that would be pointless. That is how stupid theism is because at the end of the day, all it's adherents have is a book of plagiarised crap.