The Jewish law conatain couple of things: the Torah commandments, the Orally Torah and it's discussion in the Talmud and in the Gemara. You can't read and understand the Torah without the Orally Torah which is passed from Moses to the great Rabbis of today. In the intro of Shulchan Aruch you can find all the rabbis that the Orally Torah was passed to them from Moses who receivced it from God.
Although God spoke the Torah to all the nation but Moses taught it to the olders and to the wise and to the judges and they are the scholar ones. For example, the saying: "Eye for an eye and tooth for a tooth isn't about revenge but about money compensation between a Jew to another Jew. You can't understand it from reading in the Torah, you must have the Orally Torah to understand it. Another example is the receptions of Abraham to the envoys and the reception of Laban to Jacob. Abraham and his wife made them food and Laban kissed Jacob but the Orally Torah is telling us that Laban kissed Jacob because he wanted to search for jewels in his mouth.