Isn't it amazing how people descend on supermarkets like a swarm of locusts and buy out every crumb of chameitz as soon as Pesach is over? It defies rational explanation. I expect to eventually see someone setup a tent on Central Ave in the 5 Towns on chol ha'moed so they can camp out in front of the pizza store to be first on line to get that first pie after Yom Tov. Anyway, welcome back everybody!
"Yom ha'shmini," the day the opening of our parsha focusses on, was one of the greatest days in history. Chazal (Shabbos 87) tell us that the day had 10 crowns, i.e. there were 10 reasons why the day was special, from it being the day on which creation happened to it being the day in which the mishkan was inaugurated and Aharon began serving as kohen gadol. It was opening day x10. Yet Rashi writes in Yisro (Shmos 24:9) that Nadav and Avihu were really chayav misa back then for improperly gazing at Hashem's presence (whatever that means) but Hashem let the cheit go until our parsha so as to not disrupt the joy of kabbalas haTorah. "Yom ha'shmini," as joyous and great as it was, could be marred by Nadav and Avihu's death, but the simcha of Torah cannot be disturbed. There is no simcha as great as the simcha of Torah.
During the 7 days of milu'im Moshe brought korbanos on behalf of Aharon and his children. Among them was a par offered as a chatas, which was meant, explains Rashi (Shmos 19:1), as a kapparah for cheit ha'eigel. In our parsha we read that on yom ha'shmini Aharon himself offered the korbanos, and among them was an eigel offered as a chatas meant, as Rashi (9:2) explains, as a kapparah for cheit ha'eigel. Didn't we do that already? Why did Aharon need to bring another chatas for kapprah for cheit ha'eigel when korbanos had been offered for that purpose during the milu'im?
Maharal in Gur Aryeh answers (not exactly in these words) that it's like a minor league player who is the talk of the triple A league, but then makes it to the majors and finds his ability questioned on the back pages every time he has a bad game. Those very same back pages of the newspaper had only the highest praise when he was in the minors, so what changed? The answer is simple: welcome to the big leagues. Stepping up to the next level invites greater scrutiny and demands greater accountability.
The Midrash darshens "u'Pharoah hikriv" by Yam Suf (why hitpa'el?) that we just read at the end of Peach as telling us that Pharoah's pursuit of Klal Yisrael inspired them to teshuvah more than any words of mudsar or chastisement could have done. But what was Klal Yisrael doing teshuvah for? They had just come from offering korban pesach, doing milah, experiencing yetzi'as Mitzrayim, not from any wrongdoing (see Imrei Emes)? Perhaps the point is the same: davka because they were now free from Egypt, free from the environment that dragged them down to sin, Klal Yisrael had a greater responsibility to introspect and improve further. Climbing to the next level does not absolve one from obligation -- it creates greater obligations.
"Yom ha'shmini" was a different league from the 7 days of milu'im. Kapparah that may have sufficed in the past now needs to be re-examined and taken to another level.
I have the old edition of the Maharal at home and that's how I understood the point when I read it, but then I saw in Rav Hartman's footnotes in the new edition that he understands it a bit differently. Maharal holds that there are certain pivotal moments in Jewish history. Just as we hopefully want to seize those moments for good, the yetzer ha'ra works even harder than usual to thwart us and turn those moments sour. That's why we find that during what should have been a time of spiritual greatness, matan Torah, there was a cheit ha'eigel. Precisely because there was such positive energy, there was a counterbalancing of explosive negative energy that the yetzer marshaled to thwart us. So too, at the time of "yom ha'shmini," because this day was a pivotal moment, an extra kapparah was needed so as to not have a recurrence of an eigel situation.
Perhaps this sheds light on why Moshe reacted with anger when he saw what he thought was an error being made and korbanos being disposed of and not eaten after Aharon and his sons became aveilim. R' Simcha Zisel of Kelm puts it in context: Aharon has just lost his sons; his other children have lost their brother. Even if they were in error in disposing of the korbanos, wouldn't it be understandable given their grief? Did they deserve to be questioned so harshly? Yet the greater context is that this is a one time pivotal moment in Jewish history, a day that can never be duplicated. Evil lurks waiting to once again spoilt the show. As sensitive as he was to his brother's and nephew's plight, Moshe was also sensitive to history hanging in the balance.
Speaking of auspicious days in Jewish history, this is a great article by Shmuel Sackett.