The plain verse of Exodus 24:18 is almost flat. Moses entered the cloud and went up the mountain, and he was there forty days and forty nights. The Targum Pseudo-Jonathan cannot leave those forty days unexplained. What was Moses doing up there?
The Targum answers with a phrase that reframes the whole encounter. Moses was learning the words of the Law from the mouth of the Holy One, whose Name be praised. It was not a meeting. It was a tutorial. The Creator of heaven and earth was personally teaching Moses, word by word, the entire Torah.
The Talmud in Menachot 29b preserves a famous scene of Rabbi Akiva explaining the crowns on the letters of the Torah, and Moses, transported forward in time, sitting at the back of the study hall and failing to follow along. That later picture has its root here. The Torah that Moses received was not a finished book handed down. It was a living instruction, taught mouth to ear, with room for every future generation's questions already built into it.
Forty days. The number echoes the flood that reshaped the world, and the forty years Israel would later wander in the wilderness. It is the span of full transformation. Moses entered the cloud as a prophet. He emerged as the teacher of Israel, carrying in his memory every word the Holy One had spoken.
When tradition calls him Moshe Rabbeinu, Moses our Teacher, this is the credential. He studied Torah directly under the Author. The takeaway is an invitation: every hour a Jew spends learning Torah extends that forty-day classroom by one more lesson.