Why would god's only way of communicating with us be a book written by men?

What about all the people that cannot read, are they suppose to just believe everything they hear? And even for people that know how to read, are they just suppose to believe everything they read in an old book written by primitives? And which religious book is suppose to be the correct one, they all claim to be divinely inspired? If there is a personal god, why doesn't he just speak to us in an audible voice? Why doesn't he or she just tell us what it wants from us in an undeniable voice?