The Torah was given with great excitement and drama: There was thunder, lightning, fire and an extended shofar blast. The people felt they had died and returned to life, and were very fearful.
Hashem Himself actually communicated the mitzvos directly to the people, as the Torah states (20:1): “Elokim spoke all these words…” The people reached a heightened state of prophecy in order to perceive Hashem’s commands directly.
How many of the ten commandments were said directly by Hashem to the people? The Gemara states that the first two were heard directly from Hashem. (Horiyos 8a and Makos 24b; see further Rebbenu Bachya in the name of the Moreh Nevuchim.) This is derived from the wording of the commands: Only the first two are stated in the first person, e.g. “I am Hashem…” After that, Hashem doesn’t refer to Himself as “I”. (Ramban)
However, the Ibn Ezra questions this. The verse says explicitly: “Elokim spoke all these words…” implying that Hashem Himself spoke all ten. The Ramban therefore concludes that Hashem actually said all ten, but the people were unable to understand more than the first two; Moshe had to explain Hashem’s intent for the other eight.
Emunas Olam
Earlier, Moshe had had doubts as to whether the people would trust him. Here, Hashem assures him, “They will believe in you forever.” (Shmos 19:9) What is this ‘eternal faith’ referring to?
The Rambam (introduction to Brochos and Moreh Nevuchim, also Ramban in our parsha) says that false prophets who contradict Moshe’s Torah will not hold eternal sway over the people. All the Jewish People beheld clearly Moshe’s agency as the one who delivers and explains Hashem’s words.
Moshe said, “don’t be afraid, Hashem came in order to test you.” (20:17) What was the test? The Chidushei Hagrim (in the name of the Rambam) writes that the test will come in later generations when false prophets will challenge the Torah. Will you remember what you yourself perceived at Mount Sinai?
The Promise at the Burning Bush; Three Months After Pesach
Moshe had many doubts and questions when he first spoke directly to Hashem. Why did the people deserve the miraculous Exodus?
Rashi (3:12) explains that Hashem said: “What is the merit of the Jewish People that entitles them to leave Mitzraim? I have something very great: Three months after they leave you will serve Hashem on this mountain (Mount Sinai).” This must refer to the receiving of the Torah; but what does Rashi mean, “three months after they leave”? Shavuos (which celbrates the giving fo the Torah) is not even two months after Pesach!
See Sifsei Chachomim (Ibid.): The seventeenth of Tamuz is three months after Pesach! On that day the tablets upon which the commandments were engraved were to be given to the people. Rashi is referring to the giving of the tablets, not the hearing of the mitzvos from Hashem.
Why does Rashi refer to the giving of the tablets and not the dramatic day of the giving of the Torah on Shavuos? Initially, the commands were heard orally; the tablets were the first text.
There are two aspects of transmission. The Rebbe puts all his heart and soul into transmitting the Torah to his students until they virtually reach the same level as the Rebbe himself. This is very hard to do; few teachers reach such a level of transmission. The second aspect is when the student takes what is presented, and applies himself so fervently that he acquires Torah with his own efforts. For this you need a text. Rashi is telling us that the merit of Torah — the merit for which the Jews were redeemed from Egypt — could not be complete until they had the text of the tablets. (Asifas Shiurim, introduction to Bava Kama)