When Moshe saw the burning bush HaShem appeared to him בלבת אש (the brightness of the fire). בלב"ת ב' לוחות ב' תורות. At Har Sinai during the 40 days Hashem taught Moshe both the Written and Oral Torah. During the daytime HaShem taught Moshe the Written Torah and at night He taught him the Oral Torah (Medrash Rabbah). This is way from Above to Below.
Thus, Moshe understood that the Written Torah preceded the Oral Torah. את גדלך – Written Torah and then ואת ידך החזקה – Oral Torah. Moshe states this same concept here in Devarim 5 היום הזה ראינו את כבודו ואת גדלו – Written Torah ואת קולו שמענו מתוק האש – Oral Torah; and “who is like G-d בשמים – Written Torah ובארץ – Oral Torah.
Moshe pleads “please let me cross over to the Land.” The Torah of Eretz Yisrael is not like the Torah from Heaven. First Moshe mentions הארץ הטובה (Oral Torah) and then והרק הטוב (the Written Torah). The method in Eretz Yisrael is from below to above, which Moshe wishes to experience.
HaShem answers Moshe רב לך, sufficient it is for you. You do not need this Torah of below to be Above (אור החוזר); the Torah from Above to be below (אור ישר) is sufficient. As the Zohar explains that HaShem next told Moshe to write this Shirah (Torah) indicating that HaShem is praising Moshe like one of the angles that can transmit from Above to below. Therefore, HaShem next tells Moshe to command to Yehoshua וחזקהו (the Written Torah) and then אמצהו (Oral Torah).
