“After the utterance of the Aseres Hadivros [the Ten Commandments], Hashem taught Moshe Rebbenu the entire Torah over a period of forty days and nights. He acquired the luchos (tablets of stone), which were the miraculous work of Hashem.
The Miraculous Tablets Made by Hashem
The Rabbis tells us that all the texts were taught to Moshe on Mount Sinai. Originally, they were contained within the luchos — miraculously, by gazing at the tablets, one could understand the written Torah and all the Rabbinic texts without effort…
However, after they made the Eigel Hazahav (Golden Calf), …The letters flew off the first tablets. They were heavy, and Moshe dropped them. It was the Torah Sh’ba’al Peh [the Oral Torah] which flew away!
This is why the luchos were too heavy — it’s impossible to have the Torah bichsav [the Written Torah] without the Torah Sh’ba’al Peh. (For example, we wouldn’t know how to make tefillin or tzitzis, or which fruit to use with the arba’ah minim!)
…after breaking the luchos, Moshe had to replace them. These second, man-made luchos, did not have the power to convey the entire Torah. Now, there would be two distinct aspects of Torah. [ the written](represented by the luchos), [ and the oral] the Talmudic explanations…
The Written Torah Versus the Oral Torah
The reason for this new division is as follows: If it weren’t for the cheit of the Eigel [sin of the golden calf], no nation would have the power to rule over them. However, now that the sin had been committed, it was decreed they would … go into exile… It was necessary to establish the Bris Hatorah [The Covenant of Torah], so that Yisrael would not be lost among the nations.
…only a small portion of the Torah would be written (which the nations, would, indeed, have translated). The bulk would… be given orally from teacher to student in a difficult format, and would remain uniquely Jewish. Now the Torah Sh’ba’al Peh would take effort and hard work, unlike the case with the first luchos, where everything was in written form, perceived miraculously by gazing at the text.
…The …Bris Hatorah, is the Torah Sh’ba’al Peh (the oral traditions)”
– Excerpts from the article