And you, bring near to yourself your brother Aharon, and his sons with him,... to serve Me as Kohanim. (28:1) Here, Hashem designates Aharon and his sons to serve as Kohanim. Moshe Rabbeinu was just as worthy as Aharon to become a Kohen, yet Moshe was the one who installed Aharon as Kohen, as well as his children. Moshe was a devoted servant of Hashem, and always followed the will of Hashem. But one might ask: Moshe would have obviously been the best candidate for the role of Kohen Gadol. The answer may be: True leadership in Klal Yisrael consists of praying to Hashem for His chesed and goodness to Yidden.
We see in Tehillim:
Moshe and Aharon among His priests, and Shmuel among those who call His name, call out to the Lord, and He answers them. (99:6) Here we see that Dovid Hamelech equates Moshe and Aharon as being Kohanim. Dovid describes Shmuel Hanavi as the one who calls His [Hashem’s] name. Yet Dovid states that all three have the power of having their prayers answered. In prayer, there are many different approaches. Every tzaddik has his Avodah in Tefilah. Moshe and Aharon were always praying for Klal Yisrael. Moshe prayed as a leader, whereas Aharon prayed as a Kohen. Shmuel Hanavi prayed as a prophet. All these avenues of Tefila are precious to Hashem. Moshe was the leader of Klal Yisrael, Hashem derived pleasure from his Avodah. Hashem wanted the Avodas Hatefila from Aharon who was Kohen. Hashem wanted the Avodah of the Novi, Shmuel. Today, Hashem wants our Tefilos, as Dovid Hamelech says:
He, Hashem has turned to the prayer of those who cried out, and He did not despise their prayer. Dovid concludes: Let this be inscribed for the last generation. (102:18) The last generation is ours! As we approach the days of Purim, we are taught that the tefilos on this day do wonders. With preparations and a straight mind, go full force and let out your heart with all your prayers. The Chidushei Harim of Gur used to say that the Satan knows this secret and uses different ploys to distract the Yidden from praying in Purim.
(Yehuda Z. Klitnick)