Shemini. Was It Sinful or Meritorious

Moshe told Aharon that Nadav and Avihu were chosen because they were greater than them. Aharon heard what Moshe said and was comforted.  On the other hand, we have clear statements in the Torah, amplified innumerable times in Chazal, that Nadav and Avihu had done something wrong. So what is the story here? Were they chosen to be korbanos because they were so great and righteous, or did they die because of their failings? Was it punishment or reward?

Additionally, it appears that the consolation of Aharon only enabled him to continue functioning pursuant to the commandment to not be meisi'ach da'as. Klal Yisrael, on the other hand, was allowed and indeed commanded to cry and mourn for the fiery death of these two great men. So it seems that Moshe Rabbeinu saw a need to comfort Aharon, and his words did have an effect, but despite the truth of those words, there was still an overwhelming reason to cry and mourn.

I think that you can't escape the fact that it was both. It was sinful and meritorious, it was punishment and reward. Apparently, a human who is judged imperfect only in light of the highest middas hadin can be chosen as a korban davka because of that combination of exaltedness and imperfection. Punishment because one was zocheh to perfect middas hadin is indistinguishable from reward. This was the consolation of Aharon.

And I think that despite what might be an initial negative reaction to the application of "two dinim" to something so deeply emotional and human, I think that you also have to accept what Rav Povarsky says about two dinim in aveilus: one in sympathy with the torment of the human soul after death, and the other mourning for the loss of personal contact with the niftar. The din Torah of aveilus is the first, and the personal aveilus is the second. A tzadik gammur might not elicit the first, but will doubly elicit the second.  Here, the fact that their death was the result of their inconceivably high darga meant that the first din of aveilus was not relevant, and so Aharon was told to force himself to not think about the personal loss he had experienced - איבעי ליה ליתובי דעתיה (Sukkah 25b). Klal Yisrael certainly needed to mourn the terrible personal loss they had suffered, both out of their own emotion and to show respect to Nadav and Avihu - calm serenity would show they felt that it wasn't a big loss.