Most books are written in such a way that everything that the author wants to communicate is spelled out clearly. The Torah is not such a book. Talmudical hermeneutics (for instance, the 13 rules of Rabbi Ishmael) are necessary to understand what the Author wanted to communicate with respect to halacha. My question is why was the Torah written in such a fashion?
Like can been found in Sefer Orot HaGra, on the section dealing with Torah, the Vilna Gaon expresses the idea that all events and all people from the beginning of time to the end are contained within the five books of Moshe. He explains that all these hermeneutical details are necessary in order to include every detail of creation.