Aharon was affraid to approach the altar, and Mosheh said it was Aharon's very fear that made him worthy to approach the altar.
Thus Aharon, and all Tzaddikim, recognize that they must always approach the altar, always finding some deeper sin within them that still needs to be rectified.
It is this deep care and concern over even the smallest matters that endears the Tzaddikim in the hearts of the people and awakens all who see the Tzaddikim to teshuvah, avodat HaShem and mesirut nefesh.
It is through this same deep regret and sorrow over even the smallest matter that the Kohen literally, and the Tzaddik figuratively is able to slay the Egel haChatat, the Egel HaZahav, the golden calf. (By glorifying HaShem's name in public and raising Bnei Yisrael's hearts to their Father in heaven)