What does it mean to interpret the Bible literally? It means to read the bible and believe what it is saying.
People who take the bible literally would (for example) claim that the Earth was created in 6 days. Time is relative to speed, and the speed has been slowing down. Why couldn't 20 billion years happen in a day?
That the Genesis story is not a parable and that it's historically accurate; however these are the types of people I consider "hard core" literalists. Whereas some people would rationalize the story by saying that 6 days is not the same as 6 days is now. If you would like, research the speed of light slowing down.
Non-literalist would say that the story is to be reflected on and not taken as actual fact. They point to the words in the bible about Jesus: Ok.
Matthew 13:34 NIV: Jesus spoke all these things to the crowd in parables; he did not say anything to them without using a parable. Yes.
This causes a problem with taking the bible literally, how can you take the stories literally when Jesus himself spoke in parables? It becomes a reciprocating problem. Not if you understand the parables.
The problem is, where does it stop? For example, if I believe that the world wasn't created in 6 days, or that Jesus didn't really walk on water, where do you take the bible literally? You've just jumped down the rabbit's hole. Sure, logically until more is thoroughly explained things that appear unbelievable, then become logical. I became an Atheist, after reading Genesis as well. I overlooked the six day start, but got snared by Cain running into the mountains to marry his wife. I was like no way did dude marry his Mom on a mountain. That seemed to me illogical, I would rather yank out my eyes and sand off my tongue, then marry mo Mom. Interesting thing happened though. I was writing a computer program that take sections of DNA and meld them together. The process I found exciting, I liked the idea of creating a real dragon to kill. Note: I'm not so into that idea anymore.
Anyways, In my DNA research I found that paternity tests where not limited to Father Son. You could do Grandpa to Grandson, Great Grandpa to Great Grandson, and 1000 Greats Grandpa to 1000 Greats Grandson. I found that it pointed to One Man, not once but twice. The first branch being Adam, and the second being Noah. So I did a little more research and found out that Cains sisters where not mentioned. In fact very little history about women was recorded at all. So the Idea of Cain grabbing a sister and running seemed more realistic. Not that I have any sisters, but I watched a lot of Porn in my life, and Brothers and Sisters do do it.
So, somethings in the bible are to be taken literally and something are to be taken as a parable. Which passages are which? Who knows, we'll find out when we get there. This does complicate the teachings, I'll not deny, but I have found that all the parables are analogical stories. So a simple, "Is he making an analogy?" question simply needs asked before deciding the correct interpretation. Also, the answer key as to understanding the parables was given within the text, so anyone really listening to what he was trying to say would see the pure truth to what he was revealing. (Matthew 13:35)
So what about the Six Days? I recommend watching a movie called "The Genesis Code" I highly suggest you watch it. It shows how both Science and 6 Days are both correct with simple logic. Personally I feel that Correct Science will have Religion back it up, and Correct Religion will have Science back it up, for science is only a description of what God does, and how he does it.
Why should it be taken Literally? For Truth to be True, it must describe itself truthfully, and it must Truly represent Truth. An incorrect representation of the truth is not True. Therefore since the Position that God has taken as "described" by himself, is that he speaks Truth, if that where to be True. Then all that is said is a True representation of the Truth. Not literally taking what is said, is by nature a misrepresentation of the Truth and is not True. If you do not Truly do this, then you cannot Truly get the Truth that he is trying to deliver.