When did they say this to Moshe?
Rashbam: After they heard the Aseres ha'Dibros from Hashem. 1
Rashbam: Had they not said it, it seems, He would have told them the whole Torah.
This request is also described in Devarim 5:22 . As Moshe retells, "For what flesh has heard the Voice of the Living G-d, speaking from amidst the fire, as we did - and lived?" (Devarim 5:23). Chazal expound that whereas the other nations heard and their souls departed them, Yisrael heard - and lived. Why did this occur?
Maharal (Tif'eres Yisrael Ch. 31, p. 92): Torah is from Hashem; one who possesses the Torah attaches himself to Hashem, and this brings life. Approaching Hashem in an improper manner, on the other hand, brings death. Thus the Torah is simultaneously an elixir of life for Yisrael, who transcend Chomer, but a potion of death for the nations who are inclined towards Chomer. 1
See Shabbos 88b - The souls of Yisrael also left them upon hearing the Word of Hashem, but Hashem brought down upon them the dew of Techiyas ha'Meisim and revived them. Maharal (loc. cit.) - At the level of Hashem's existence, nothing else can exist (and as above, this direct communication from Hashem joined us like a partnership). But Yisrael was connected to Hashem on the highest plane, from which life and Techiyas ha'Meisim emanate. (For more about Yisrael's unique Tzurah according to Maharal, see Shemos 1:1:2.8 and 14:5:4:4 ).
