To say a book is the word of a god is a pretty strong statement. Those who are skeptical about the claims of religions often criticize parts of what books like the Koran and the Bible say. While these questions are important, people also need to think about what these books do not say when considering their potential to be divine word.
It is impossible for people to even begin to comprehend the kind of wisdom a being with the power to create the universe would have. Although human beings have amassed a significant body of knowledge, it still is a long way from unlocking all the secrets of the universe. There are just so many things a creator of the universe could tell people. However, human wisdom has always expanded through trial, error and research and not through any of the books that are supposed to be divine word.
Some people do claim that parts of these books do have scientific and other knowledge hidden in their pages. However, it seems odd that a god would reveal things to people in ways that would only be apparent after the discoveries had been made. The fact is that patterns can be found in any book if people look hard enough. Therefore, unless it can be demonstrated that a book clearly and directly says something that was not known at the time, such claims should not be taken seriously.
While they may seem obvious to people now, humanity has already learned many things the hard way that certainly could have been stated in these books as moral or other teachings. For example, slavery is never clearly condemned even though doing so would have saved literally millions of people from the most horrible fates. People often find ways to conveniently ignore what their religions teach, but there is no arguing that a clear condemnation of slavery (it can certainly be argued that they condone it) in books like the Bible and Koran would have made a huge difference. Very pious people owned and practiced slavery almost until modern times.
Knowing how people are, it would also seem that any god would have clearly and unequivocally stated that things to include child abuse or beliefs such as racism were wrong. There is no telling how attitudes would have changed and human misery averted if these things had been included in holy books.
Then, there are the kinds of practical knowledge that could have made such a difference. For example, how many lives could have been saved if people had learned germ theory from their holy books long ago rather than from scientists in modern times? The plagues that repeatedly annihilated huge portions of the populations of many parts of the world could have at least been made a lot less lethal if people understood things like sanitation. Not only could have lives been saved, but so many human beings could have avoided painful medical treatments that frequently only made things worse.
Then, there is the mental anguish caused by ignorance. For example, women were often blamed for giving birth to deformed children since it was thought that evil thoughts during pregnancy caused the deformities. In other cases, the mentally ill were thought to be possessed by demons and were tortured in an attempt to drive them out.
It also seems rather odd that neither the Bible of the Koran said anything about the new world in the Americas. If the author of these respected books knew all and wanted its followers to spread the faith, why would not these books tell them there was a whole new world of souls to be saved (and tell them to spread the faith in a humane way)?
While there are limits to what any book could tell people, especially in more primitive times, there are certainly plenty of ways they could have been made a lot more enlightening. Of course, useful moral teachings can be found (along with some more questionable ones) in religions, there is nothing that even those living in the most primitive societies could not have figured out on their own. Would not a god want to enlighten people in ways they could not figure out so easily? That would not only help his creations, but it would also gain followers for the faiths that follow these books.
Although it can be argued that it is not the responsibility of a god to teach people anything in his books, it does seem to go against logic that one would not.