Maharal in Gur Aryeh here disagrees with Rashi instead of defending him as he usually does. He quotes Toras Kohanim which explains that the point of the pasuk is not that Aharon obeyed, but that he did what he had to b'simcha, as if he had been commanded to do so directly by Hashem. It is much harder, says Maharal, to take orders from someone else - a middleman - than to follow orders when they are given to you directly.
According to this pshat the language of the pasuk is meduyak. It's the "asher tzivah Hashem b'yad Moshe" which is the challenge -- the fact that the instructions were given through an intermediary.
Much of Torah is transmitted to us via intermediary. Torah sheba'al peh, mesorah, is all about following the instructions of Hashem as relayed to us by Chazal.
Klal Yisrael willingly accepted Torah she'b'ksav. The threat of kafah aleihem har kgigis was because Torah she'bal peh was a harder sell.
The gemara writes that true complete acceptance of Torah came at the time of Purim.
Just as the Toras Kohanim learns that Aharon's simcha reflected a complete kabbala of the ba'al peh mesorah given via Moshe, so too simcha Purim reflects our complete kabbala of the same.