Midrasch zu Dewarim 9:1

Why did [Moses] see fit to say “Hear O Israel” at this point? The Rabbis say, “To what can this be compared? To a king who betroths a noblewoman with two pearls. She loses one of them. The king says to her, ‘You lost one, I will guard the other!’ So did the Holy One, blessed be He, betroth Israel with ‘Naaseh v’Nishma’ - ‘We will do and we will hear.’ They lost the ‘Naaseh’ at the Golden Calf. Moses said to them: You lost the Naaseh, guard the Nishma!

"cities great and fortified in heaven": R. Shimon b. Gamliel says: Scripture (here) speaks hyperbolically, as it does in (Ibid. 9:1) "Hear, O Israel, you are crossing over the Jordan this day." But when the Holy One Blessed be He says to our father Abraham (Bereshith 26:4) "And I will multiply your seed as the stars of heaven," and (Ibid. 13:16) "I will make your seed as the dust of the earth, so that if a man can number the dust of the earth, so will your seed be numbered" — this is not hyperbole. (Devarim, Ibid.)