Komentaryo sa Levitico 10:1: Kli Yakar, Sforno, Or HaChaim & Rashbam

“And they offered before the Lord strange fire, which He had not commanded them.” Regarding the nature of this sin, there are many opinions in the Yalkut (Shemini 554). It concludes in the name of Rabbi Mani that they entered intoxicated with wine, and because they entered without washing their hands and feet, and some say they were lacking garments, specifically the robe, and some say it was because they had no children, and some say because they did not marry wives, and some say because they ruled on matters of law in the presence of Moses their teacher, and some say because they were walking and saying, “When will these two old men die, and you and I will lead the congregation with authority,” and some say that the sin of the golden calf that Aaron made caused their punishment, and they expounded on this the verse he shall pay two to his fellow (Exodus 22:9). And all these opinions, even though they have some support from other verses, nevertheless this verse contradicts all those opinions, as it is said, And they offered before the Lord strange fire, which He had not commanded them, which implies that they had no other sin except this one.

ויקחו שני בני אהרן איש מחתתו, they thought that just as after the daily communal offering which was accompanied by the manifestation of G’d’s Presence as we know from Exodus 29,42 עולת תמיד לדורותיכם פתח אהל מועד לפני ה' אשר איועד לכם שמה, “the regular communal burnt offerings for your generations in the presence of the Lord, where I will manifest Myself there,” there would come the incense, so it would also be in order on this occasion to present a new incense offering honouring the manifestation of the Lord to the whole people and in honour of the heavenly fire having descended.

It seems to teach that the place of their error was for two reasons. The first was that in becoming priests, they erred in their service, and this ( is implied in the text) beginning by saying they were 'sons of Aaron'; the two of them (thought) they were great in deeds and should be weighted like Moses and Aaron [Torat Kohanim Achrei Mot 53]. And as the Zohar teaches, they were on a high spiritual level in the realm of deeds, hence they were called ('sons of Aaron') Nadav and Abihu, and this trait is not so for Elazar and Itamar (the Torah does not refer to them as 'sons of Aaron'); they too are 'sons of Aaron', but are not at the spiritual level themselves that Nadav and Abihu were. So too we find this explanation where (the Torah) says