In Parshat Behaalotcha, Aharon HaKohen is appointed to the task of lighting the Menorah. He was so overjoyed that according to Mefarshim, even though he had the right to forward the mitzvah to others, he kept it for himself all his life. He had an intense connection to this Mitzvah over all others, which is ironic considering that he was given this mitzvah only as a kind of consolation prize.
When all the other heads of the tribes were giving their inaugural gifts to the Mishkan, Aharon felt left out because he could not give one himself. To make up for this disappointment, he was given the Mitzvah of lighting the Menorah.
One might wonder, though, how these two Mitzvot could be comparable. How are the inaugural sacrifices the same as the lighting of the Menorah? We can answer that both were commandments from Hashem (see 7:11), and both were involved with the functioning of the Mishkan.
What made this Mitzvah so special that Aharon kept it all his life? Ramban points out that this Mitzvah was going to be an inaugural mitzvah later, in the story of Chanukah. This Mitzvah of lighting the Menorah was not just a one-time Mitzvah, as the offerings were. It had an unlimited time frame, and this was what Aharon appreciated about it and why he valued it so much.
Aharon wanted to give an offering of his own, but instead he held his needs in abeyance and offered others’ sacrifices, as Hashem asked. This kind of selflessness earned him one of the most valuable Mitzvot of the Mishkan.