Parshat ואתחנן really begins Moshe’s final charge to the Jewish people. In Parshat דברים, we are given a historical account of what we went through in the desert with all of its difficulties. In this Parsha, there is specific instruction.
Moshe reminds the עם what their eyes witnessed at הר סיני. This was an event unparalleled in human history. It was the day when we officially became a nation.
But there is also an important, often overlooked Pasuk that is mentioned. It is written. ואותי צוה ה׳ בעת ההיא, “And I was also given a command at that time.”
ללמד אתכם חוקים ומשפטים,
“To teach you the laws and statutes.” Rashi explains that this was the defining moment when the תורה שבעל פה, the Oral Law was given. And this where Moshe became משה רבינו, Moshe, our teacher.
He, and the Rabbis that followed, were to be the transmitters of Torah. The Written Law and the Oral Law are one and the same.