Nadab and Abihu raised a disturbance between the congregation of Israel and the Holy One, Blessed is He (Zohar 3:38b).

Moses and Aaron were going their way, and Nadab and Abihu were walking behind them. Said Nadab to Abihu: "When will these two old men die, and you and I lead the generation?" The Holy One said to them: "Let us see who will bury whom" (Sanhedrin 52a).

Aaron’s sons died because of four things: entering the Holy of Holies; offering a sacrifice that they had not been commanded to offer; bringing an alien fire; and failing to consult each other (Vayikra Rabbah 20:8).

The deaths of Nadab and Abihu were recorded in a few places in the Torah to teach that there was sadness in the presence of God about them, for they were beloved by the Lord (Bamidbar Rabbah 2:23).After the erection of the desert Tabernacle, Aaron and his sons, Nadab and Abihu, were consecrated as the Priests (kohanim) of Israel. The sacrificial service was entrusted by Moses into their hands. Unfortunately, amidst the ceremony of such awesome religious joy, Nadab and Abihu "each took his fire pan, placed incense upon it, and brought before the Lord an alien fire that He had not commanded. A fire came forth from before the Lord and consumed them, and they died" (Leviticus 10:1-2).

It is a disturbing as well as confusing narrative. Particularly as Moses calms his bereft brother with the Divine explanation: "Through them who are nearest me I will be sanctified, and before all the people I will be glorifed" (Lev.10:3). The text tells us that Aaron "held his peace," but, more likely, he was dumbfounded. What brought about the deaths of these novitiates? The commentators offer numerous possibilities. Some take the passage literally: that is, Nadab and Abihu erred in bringing their own incense into the Holy of Holies. Some suggest that the two sons of Aaron, so moved by the splendiferous Heavenly fire God had earlier bestowed upon the Israelite offerings, wished to reciprocate with a display of their own love of God. The offering of incense was their means of expressing this boundless devotion, but that was not according to script(ure).

The Midrash, trying to shore up the bewildering text and the terrible harshness of the punishment, suggests that Nadab and Abihu were letzim ("scoffers") who resented the authority invested in their father by Moses. Thus the plotting and scheming to undermine the "older generation." Whatever their motives, it is not a happy scene in Israel’s history. The dutiful Aaron, who had earlier served as the people’s kapporah ("expiatory sacrifice") during the building of the Golden Calf, now must humble himself again. It is a bitter pill, and with respect to the later fate of his other two sons, Eleazar and Ithamar, it becomes harder and harder to swallow.