In the ancient Middle East, words were considered to be your "bond". This is where we get the saying "He's as good as his word". Therefore if God said something about himself, he can only be telling something true about himself because God, being truth, can only tell what he is.

In those times, the actual writing down of words was done ONLY to record great military conquests done by kings and pharaohs, great harvests and famines, laws concerning government, due to the lack of writing material (ink, papyrus, animal skins, clay tablets and walls). Since the writing of words was seen so dear, to destroy these writings was akin to destroying that person that the recording was about. This is why there's so little accounting about the "Habiru" (Hebrew) people in their records: they thought that wiping them from their records would help to wipe them from the face of the earth. God wrote his Ten Commandments on STONE to symbolize the unchangeableness and unbreakableness of his nature through his words.