The parshah begins with Moshe Rabbeinu cajoling Aharon to enter the Mishkan in order to perform the avodah: "Come near to the mizbeiach and perform your sin offering and your burnt offering and the sacrifices of the nation" (Vayikra 9, 7). Rashi explains that Aharon was too embarrassed to enter the Mishkan, and therefore, Moshe had to cajole him to enter: "Why are you embarrassed? You were specifically chosen to perform this avodah." The Ramban elaborates that Aharon's embarrassment and hesitation to enter the Mishkan stemmed from the role that he played in making the golden calf. To which Moshe responded, "Have a proud spirit and come and perform the avodah."
Rav Wolbe (Shiurei Chumash) makes an interesting observation. In Pirkei Avos (4, 4) it says that one should be exceedingly humble. With this in mind, we could understand Aharon's uneasiness in accepting the position consigned to him. He felt that he was unworthy for the lofty position of bringing sacrifices before the Creator of the world. If so, why did Moshe tell Aharon to act haughtily and perform the avodah, against the dictates of Chazal? The answer is that although one must be exceedingly humble (as the Mishna in Avos states me'od me'od, a terminology found almost nowhere else in Chazal) nevertheless, there is a limit to the amount one should exercise this trait. If one's humility inhibits his avodas Hashem then he has surpassed the proper application of this middah. Moshe was telling Aharon that if he was specifically chosen for this position, then this is not the time and place for humility.
This is an idea that has a practical application for each and every one of us. Many people shy away from learning mussar because they have no interest in highlighting exactly how bad they are. Even those who do learn mussar often fall into depression after unearthing how many negative traits they possess. The truth is that mussar study is only effective for a person who is already cognizant of his abundance of positive traits and awesome innate greatness. Rabbeinu Yonah makes this abundantly clear at the onset of his Sefer Sha'arei Avodah:
"The very first entranceway (into avodas Hashem) is that one who wishes to serve Hashem must know his own worth, and be cognizant of his caliber and the caliber of his forefathers, and their greatness, importance and how beloved they were to their Creator. And he must constantly strive and strengthen himself to maintain this caliber. And he should think to himself, 'A great and important person like myself today, who has lofty and awesome positive attributes, and I am the son of great people - the son of kings from the past - how can I do such a terrible thing and sin before Hashem.'" Humility would only be detrimental to such a person. He would recoil at the thought of serving The Creator in his lowly state. Such behavior would send him down the ladder of avodah instead of up the ladder (Alei Shur vol. II pg. 160).
Mussar study is imperative for our self improvement. However, knowing and internalizing our ma'alos takes precedence to studying mussar. Take a piece of paper and write down at least twenty ma'alos that you have. Only then should you proceed to the Mesilas Yesharim for a healthy dose of mussar!