why do christians think we know God? well thats not an answer i can give you if you have no faith. let me ask you this, from the points you made in your own words of this post you kept asking why God would do this or that or why would He create us, the world, the bible and see what we would do? from your view of God what would cause this omniscient God to even create anything in the first place? the bible doesnt really tell us why He created anything in the first place, it states we were created to worship.

let me ask you this, do you honestly think God would create everything for no purpose, to fend for themselves, without reason or direction? NO. we can not comprehend such a powerful being, your right on that part. thats why there are still so many questions when it comes to God. but, if you look at the bible you can kinda figure this out. God first created the universe and the heavenly body, i.e angels, cheribum, ect...the angels and such were created to worship and praise God, we humans were given free will to do this. maybe God started creation because He got bored? maybe we are just an experiment, maybe this is all a test.