פּירוש אויף שמות 34:8

וימהר משה, AND MOSES MADE HASTE — When Moses saw that the Shechinah passed by and heard the sound of the proclamation he immediately prostrated himself.

וימהר משה “Moses hastened;” Moses was afraid that G-d would continue mentioning even later generations than the fourth generation, he hastened to express his gratitude for what had been revealed to him at this stage. Another interpretation: Moses’ haste at this point was because he had the feeling that G-d was about to depart and he wanted to be able to offer his prayer before He departed and became hidden behind a cloud. This is also what our sages meant when they said: “when is the best time for a human being to ask for his needs? When G-d is manifestly present.” (Talmud tractate Avodah Zarah folio 7)

וימהר משה, “Moses hastened, etc.” Moses’ mind was now at rest when he heard that G–d’s Attribute of Mercy was such that His threat to annihilate the people if they sinned again did not necessarily refer to the generation that he was the leader of. He immediately expressed his gratitude by prostrating himself. He added another prayer to the ones he had already addressed to Hashem.