Issac Asimov, the athiestic Jew (that's an oxymoron) said Moses did not have enough paper (paprus) to tell the whole story (maybe he ran out if ink.) He could not possibly write down all principles of faith nor explain all prohibitions. So he vaguely said, whoever follows him, obey. He ordained Joshua to further explain, and Joshua ordained another. 40 generations from Moses, they wrote it all down in the Talmud. But the Tanakh and the Talmud still can't contain the Mind of God. Then came Kabbala. Get the point? We will never know God like He knows us.
Moshe didn't write the Torah...