John Calvin Commentary Leviticus 10:12

"And Moses spake unto Aaron, and unto Eleazar and unto Ithamar, his sons that were left, Take the meal-offering that remaineth of the offerings of Jehovah made by fire, and eat it without leaven beside the altar; for it is most holy;" — Leviticus 10:12 (ASV)

And Moses spake unto Aaron, and unto Eleazar Lest in the future the priests should transgress through ignorance, Moses admonishes them about their duty; and perhaps he was moved by some immediate reason to give these particular instructions rather than any others.

Until now they had little experience in observing the rites, and what had happened to their brothers must have made them anxious. Now, this consternation at the death of their brothers might have so confounded their senses that they could not apply themselves with the composure they should to the service of God, and thus the offering would have been improperly made.

Lest, therefore, their grief should so disturb them as to prevent the proper performance of their office, he commands them to eat what remained of the meat-offering with the burnt sacrifices. From this we gather that he sought to prevent them from transgressing on that day because their minds were occupied by their recent grief. And to persuade them to obedience, he presents to them the authority of God, to which it was fitting for the priesthood to be subject, since it was founded upon it.