Special Revelation is typically defined as when a god intervenes in the world to reveal something (or itself) to specific peoples at a specific time. I am going to extend this definition for the purpose of this post to include the teachings of Jesus, since most Christians believe he was God anyway.
In the case of the Bible, a substantial portion of the books were not written by people who had seen the events described, in fact many were written hundreds if not thousands (as with Noah's Flood and the garden of Eden) of years after the events were purported to have occurred. Let's assume for the time being that all of the stories are based on actual events, and see where we end up in terms of the believability and reliability of the stories when we get to the end of the chain.
- Eyewitnesses, or the receivers of revelation
- Re-tellers of the story
- Re-tellers of the story
- Re-tellers of the story
- Re-tellers of the story (this should be enough generations to demonstrate my point, there could perhaps be a lot more.)
- Author
- Re-tellers of the story
- Re-tellers of the story
- Copyists
- Re-tellers of the story
- Redactor
- Re-tellers of the story
- Copyists
- Re-tellers of the story
- Re-tellers of the story
- Copyists
- Re-tellers of the story
- Translators
- Commentators
- Theologian/Minister/Pastor/Priest
- Plebeian.
This is a fairly generic picture of how far removed we are from the original sources of any given Biblical text. The number of generations between each stage will differ for each individual text, and many old testament texts went through several stages of redaction (which is essentially a re-write of the text to include new content). Some Christians assert that each step of the process was 'inspired' by God, not only the authorship of it, but this simply doesn't stand up to scrutiny. The textual variants of the New Testament alone should be evidence enough to discount the idea that the re-tellers and copyists were inspired to keep the text the same. In fact many popular Christian ideas only appear in variant texts and do not appear in the majority of manuscripts. One key example of this is John 8:6-8, where Jesus says the famous "cast the first stone" line, the oldest and most reliable manuscripts do not have this story.
With the transmission process and textual unreliability out of the way, let us examine the authorship. Many of the books of the Bible were penned anonymously, and we do not have the originals (of any of them). In the case of the gospels, the names were attributed to them over a hundred years after we think they were authored. In the case of the Pentateuch, it was revised and added to many times over its history, with each step being anonymous.
Even if all of the text were completely reliable, and there were no discrepancies or errors, due to the nature of the material in the texts, they still wouldn't be believable. Textual support or 'evidence', or even eyewitness testimony is not sufficient to justify belief in miracle claims. The historical principle of analogy gives us a tool for weeding out probable and improbable events. If something in an ancient text (or a more recent text) makes a claim that an event occurs that defies what we currently know to be true, either through our own experiences, or through scientific study, then that claim is discredited. Even believers use this method (whether consciously or otherwise) when examining claims from other religions. For example, a Christian would not be likely to believe a miracle story attributed to Hercules, or to Mohammed.
An omniscient, or even just an intelligent deity would know these things, and would have an understanding that some people actual understand the nature of evidence and will not believe anything on faith. It is my position then, that Special Revelation, and thus Christianity are incoherent and unbelievable. If a deity constructed a system of religion knowing that the very credibility of his favoured method of revealing truth would come into dispute, then that deity is wilfully condemning all people who are not credulous, and is not worth worshipping. If the deity constructed the religious system, and didn't consider the fact that it would not be believable to people with a reasonable standard of evidence, then that deity is incompetent, and is less intelligent than many humans, and is also not worth worshipping.
I tend to favour the position that no such deity exists that could invent a religious system where people not only have to believe in the god purely on faith, but to know anything about said deity, they have to rely on people, who were relying on people etc. ad nauseum, also with faith alone. If a deity exists at all, it is almost certainly not one that creates a religious system that praises credulity.