"And the Lord said to Moses, ‘Go, descend, for your people that you have brought up from the land of Egypt have acted corruptly.’" (Exodus 32:7)
Rabbi Elazar said: The Holy One, Blessed be He, said to Moses: Moses, descend from your greatness. Isn’t it only for the sake of Israel, [so that you may serve as an emissary,] that I granted you prominence; and now that Israel has sinned, why do I [need] you? (Berachot 32a)
A Merit That Was Lost
This was not, G-d forbid, a punishment given to Moses. G-d said to Moses, “Go, descend from your greatness,” not as a punishment, but as a removal of the greatness he had received through the merit of Israel. Now, after they sinned, that merit no longer existed for them. (the Rebbe Rayatz)
Too Close
Why did the people not appoint Aaron in place of Moses? Because Aaron, the pursuer of peace, was too close to them, and ordinary people have no proper conduct toward someone with whom they feel excessive closeness. (Rabbi Yitzchak of Warka)
Descent in Level
Through the giving of the Torah, Moses was on the level of Adam before the sin of the Tree of Knowledge. After Israel sinned with the calf and their level fell, Moses also descended from this level. (the Rebbe Rayatz)