One of the most obviously fallacious and yet the most common of arguments for theism is the argument from scripture. This is where a theist attempts to use their scripture to claim that their particular belief system is correct. It generally goes something like this: "I know god exists because the bible says he does". Then you ask "how do you know the bible is correct?". To which the theist responds "because god made the bible".
1: The most obvious flaw is that it is circular. It assumes the truth of the bible and the existence of god simultaneously to show the validity of the bible and the existence of god.
2: All holy scriptures to date have statements that contradict what we know to be true. Such as the quran has the sun setting in to a pool of muddy water; the bible has a man living in the belly of a fish. These things are demonstrably inaccurate given what we know about cosmology and biology. Since the books are shown to be incorrect, they can not use their assumed infallibility to indicate anything.
Another variation of this tactic is to show the truth with in the text as a means to validate the text. However, this is obviously a meaningless tactic. There is truth in the stories of King Arthur. However, those truths in no way indicates that Merlin existed and that magic is real.
Another step further is the revealed truth in scripture argument. The theist will attempt to use supposedly revealed truths to show that the text was divinely inspired, if not divinely written. There are a couple of notable flaws in this as well.
1: It must be demonstrated that the authors would have been incapable of knowing the revealed truth. This is quite difficult and has never been demonstrated to be the case.
2: The revealed truth must be clear in its meaning. If you must take a liberal interpretation then it is not really revealed truth.
3: Correct speculation has no bearing on the validity of the story. In the novel Ender's Game by Orson Scott Card written in 1985, Card wrote had two of the characters using a series of fake identities over the internet posting on political forums to sway public opinion and gain popularity. Half a decade before the first forums of this nature existed, Card was already discussing them. Does that mean we should get ready for an invasion of alien "buggers"? Does Star Trek predicting flip cellphones indicate that "warp speed" is a physical reality? As such, even if the bibles did have unexplained truths in them, it would in no way strengthen the claims that we know not to be true.