מדרש אויף שמות 19:24

2) "Moses called to Aaron and to his sons": Because the L–rd honored Aaron at first, so, Moses honored him afterwards. Where is it seen that the L–rd honored him at first? In (Shemoth 19:24): "And go up, you and Aaron with you" — so, Moses honored him afterwards, viz.: "Moses called to Aaron and to his sons and (only afterwards) to the elders of Israel."

(Ibid. 24) "And the L–rd said to him: Go descend": Well have you spoken. This is as R. Yehudah says: Whence is it derived that the Holy One Blessed be He said to Moses: I will say something to you, and you will answer Me, and I will acknowledge what you have said — so that Israel will say: Great is Moses, whom the Holy One Blessed be He acknowledged? (From the above.)

Rebbi says: We would have to acknowledge the greatness of Moses only if we assumed that the Holy One Blessed be He retracted His directive. (Rather,) He spoke thus because one is prompted to zeal at the time of learning (what he must do) and at the time of acting.