Moses received the Torah from the Master of the World on Sinai and passed it down to Joshua (Tractate Avot, 1-1), as it is written- “His servant Joshua son of Nun, a lad, would not depart from within the tent” (Exodus 33-11). Joshua passed the Torah to the seventy elders, so that the Jewish people would act in a proper manner after him, as it is written- “Israel served God all the days of Joshua and all the days of the elders” (Joshua 24-31). The elders passed the law down to the prophets, and the first prophets passed it down to the later prophets, who are Zachariah, Haggai and Malachi. They passed down the law to the Men of the Great Assembly. It is from the Men of the Great Assembly that knowledge was spread throughout the generations.

The Jews were exiled in the days of King Jehoiachin of Judah, with whom the other great men from Judah and Benjamin were exiled, as well as great prophets including Daniel and his circle, Ezra the Scribe and his circle, Mordechai and his circle. Jeremiah and Baruch were also exiled to Babylonia when the land of Egypt was conquered by Nebuchadnezzar, and the whole nation went as well to Babylonia. From that day forward, wise men were always settled in Nehardea, which sits on the Tigris River. Until this day, a number of wise men reside there—the students who [first] studied the law under the prophets who were exiled with Jehoiachin. When the exiles along with Zerubbavel left Babylonia to resettle in Jerusalem and subsequently when part of the population returned to Israel with Ezra and established a yeshiva in Jerusalem, not all the Jewish population returned with them. Rather, many remained in Babylonia. Even though a new center of study was established in Jerusalem, the center in Nehardea did not cease. Wise men and prophets from both the center in Jerusalem as well as in Babylonia created laws for the Jews, and from their mouths the Jews lived for generation after generation until this day.

All people know that God revealed to Moses the explanation for every commandment and the measure of all laws and their specifics. This is the Oral Torah, its glory and its grandeur. Therefore Moses remained on the mountain forty day and forty nights and studied the explanation of the law. For if Moses did not remain on the mountain and only received the tablets, this could have been done is a short amount of time. He only remained on the mountain for forty days to learn the law and its precepts.