Rashi asks why did the Torah tell about Aharon’s duties of lighting the Menorah daily immediately following the Korbanot that the Nesi’im brought when the Mishkan was dedicated. He answers (Num. 8;2) that Aharon was disappointed that the Nesi’im brought the Korbanot and he had no duties to perform. Therefore, Hashem said to him: your task will be greater than theirs. You will light the Menorah.
It is strange that when Hashem wants to show him that his tasks are greater and more important He points to the Menorah and not that he will be going into the Kodesh Kadoshim or that he will wear the gold garments and the simple Kohanim wear plain garments. No other Kohen can do these things.
People think that a person distinguishes himself by doing something that no one else can do. The truth is the opposite. A person shows his greatness when does what anyone else can do but he does it better or does it consistently or does it regularly and does not tire from performing his task. Anyone could light the Menorah but Aharon would do it with greater Kavanah and determination than others.
When we have things to do, for example, homework or go to work or Daven or help someone, if we do it willingly and with the right spirit, then we are great. If we do it as a chore that we would prefer not to have to do, then we lose our greatness.