And Moses diligently inquired for the goat of the sin-offering, and, behold, it was burnt; and he was angry with Eleazar and with Ithamar, the sons of Aaron that were left saying:  "Wherefore have ye not eaten the sin offering in the place of the sanctuary, seeing it is most holy, and He hath given it you to bear the iniquity of the congregation, to make atonement for them before the Lord . . ."
And he (Moses) was angry with Eleazar and Ithamar, and on account of his anger his knowledge of halakhah departed from him. Rabbi Huna said, in three places Moses got angry and his knowledge of halakhah departed from him. They are (related to) Shabbat, metal tools, and the laws of an onen (one who lost a close relative but has not yet buried the dead) . . . From whence do we know this in regard to the onen? As it is written: "And he (Moses) was angry with Eleazar and Ithamar," and on account of his anger his knowledge of halakhah departed from him. Specifically, that an onen is forbidden from eating from sacrifices.
There are many rich lessons in this portion. To give greater context, at the beginning of it, Aaron's sons Nadab and Abihu are struck down by God for bringing what we only know of as a "strange fire." In the wake of their deaths, their bodies are removed, but the sacrificial ritual continues in the hands of their brothers. Moses becomes angry when he sees Eleazar and Ithamar making the sacrifices but not eating from them. The midrash suggests that in Moses's anger—presumably driven by his zeal to get this ritual "right"—he overlooks their position as mourners who cannot rightfully eat from this sacrifice. The midrash is a sound warning to us all that our anger clouds our judgment and, worse, can inhibit our compassion. These, after all, were Moses's nephews, both those lost and those mourning.
Interestingly, Aaron has been silent until this point. Much has been made about Aaron's silence in the moment he loses his sons. However, his first words after that loss come at our very incident—after Moses turns his anger on Aaron's sons Eleazar and Ithamar, it is not they who respond, but Aaron who rises to their defense. Aaron answers in verse 19: "And Aaron spoke unto Moses: 'Behold, this day have they offered their sin-offering and their burnt-offering before the Lord, and there have befallen me such things as these; and if I had eaten the sin-offering to-day, would it have been well-pleasing in the sight of the Lord?'" Aaron's answer is both a reminder to Moses of this point of law he has forgotten and a rebuke of Moses's apparent lack of compassion. This powerful exchange reminds us all to make every effort to allow our anger to give way to compassion, so that our knowledge of what is right may not depart from us.