The happiest of women on this day was Elisheba, daughter of Amminadab, for beside the general rejoicing at the dedication of the sanctuary, five particular joys fell to her lot: her husband, Aaron, was high priest; her brother-in-law, Moses, king; her son, Eleazar, head of the priests; her grandson, Phinehas, priest of war; and her brother, Nahshon, prince of his tribe. But how soon was her joy turned to grief! Her two sons, Nadab and Abihu, carried away by the universal rejoicing at the heavenly fire, approached the sanctuary with the censers in their hands, to increase God's love for Israel through this act of sacrifice, but paid with their lives for this offering. From the Holy of Holies issued two flames of fire, as thin as threads, then parted into four, and two each pierced the nostrils of Nadab and Abihu, whose souls were burnt, although no external injury was visible. 
The death of these priests was not, however, unmerited, for in spite of their piety they had committed many a sin. Even at Sinai they had not conducted themselves properly, for instead of following the example of Moses, who had turned his face away from the Divine vision in the burning bush, they basked in the Divine vision of Mount Sinai. Their fate had even been decreed, but God did not want to darken the joy of the Torah by their death, hence He waited for the dedication of the Tabernacle. On this occasion God acted like the king who, discovering on the day of his daughter's wedding that the best-man was guilty of a deadly sin, said: "If I cause the best-man to be executed on the spot, I shall cast a shadow on my daughter's joy. I will rather have him executed on my day of gladness than on hers." God inflicted the penalty upon Nadab and Abihu "in the day of gladness of His heart," and not on the day on which the Torah espoused Israel.
Among the sins for which they had to atone was their great pride, which was expressed in several ways. They did not marry, because they considered no woman good enough for them, saying: "Our father's brother is king, our father is high priest, our mother's brother is prince of his tribe, and we are heads of the priests. What woman is worthy of us?" And many a woman remained unwed, waiting for these youths to woo her. In their pride they even went so far in sinful thoughts as to wish for the time when Moses and Aaron should die and they would have the guidance of the people in their hands. But God said: "'Boast not thyself of to-morrow;' many a colt has died and his hide had been used as cover for his mother's back." Even in the performance of the act that brought death upon them, did they show their pride, for they asked permission of neither Moses nor Aaron whether they might take part in the sacrificial service. What is more, Nadab and Abihu did not even consult with each other before starting out on this fatal deed, they performed it independently of each other. Had they previously taken counsel together, or had they asked their father and their uncle, very likely they would never have offered the disastrous sacrifice. For they were neither in a proper condition for making an offering, nor was their offering appropriate. They partook of wine before entering the sanctuary, which if forbidden to priests; they did not wear the prescribed priestly robes, and, furthermore, they had not sanctified themselves with water out of the laver for washing. They made their offering, moreover, in the Holy of Holies, to which admittance had been prohibited, and used "strange fire," and the offering was all in all out of place because they had had no command from God to offer up incense at that time. Apart from this lists of sins, however, they were very pious men, and their death grieved God more than their father Aaron, not alone because it grieves God to see a pious father lose his sons, but because they actually were worthy and pious youths. 
When Aaron heard of the death of his sons, he said: "All Israel saw Thee at the Red Sea as well as at Sinai without suffering injury thereafter; but my sons, whom Thou didst order to dwell in the Tabernacle, a place that a layman may not enter without being punished by death - my sons entered the Tabernacle to behold Thy strength and Thy might, and they died!" God hereupon said to Moses: "Tell Aaron the following: 'I have shown thee great favor and have granted thee great honor through this, that thy sons have been burnt. I assigned to thee and thy sons a place nearer to the sanctuary, before all others, even before thy brother Moses. But I have also decreed that whosoever enters the Tabernacle without having been commanded, he shall be stricken with leprosy. Wouldst thou have wished thy sons, to whom the innermost places had been assigned, to sit as lepers outside the encampment as a penalty for having entered the Holy of Holies?" When Moses imparted these words to his brother, Aaron said: "I thank Thee, O God, for that which Thou hast shown me in causing my sons to die rather then having them waste their lives as lepers. It behooves me to thank Thee and praise Thee, 'because Thy lovingkindness is better than life, my lips shall praise Thee.'" 
Moses endeavored to comfort his brother in still another way, saying: "Thy sons died to glorify the name of the Lord, blessed be His name, for on Sinai God said to me: 'And there will I meet with the children of Israel, the Tabernacle shall be sanctified by those that glorify Me.' I knew that this sanctuary of God was to be sanctified by the death of those that stood near it, but I thought either thou or I was destined for this, but now I perceive that thy sons were nearer to God than we." These last words sufficed to induce Aaron to control his grief over the loss of his sons, and like the true wise man he silently bore the heavy blow of fate without murmur or lament. God rewarded him for his silence by addressing him directly, and imparting an important priestly law to him.
Aaron could not take part in the burial of Nadab and Abihu, for a high priest is not permitted to take part in a funeral procession, even if the deceased be a near kinsman. Eleazar and Ithamar, also, the surviving sons of Aaron, were not permitted to mourn or attend the funeral on the day of their dedication as priests, so that Aaron's cousins, the Levites Mishael and Elzaphan, the next of kin after these had to attend to the funeral. These two Levites were the sons of a very worthy father, who was not only by descent a near kinsman of Aaron, but who was also closely akin to Aaron in character. As Aaron pursued peace, so too did his uncle Uzziel, father to Mishael and Elzaphan. Being Levites they might not enter the place where the heavenly fire had met their cousins, hence an angel had thrust Nadab and Abihu out of the priestly room, and they did not die until they were outside it, so that Mishael and Elzaphan might approach them. 
Whereas the whole house of Israel was bidden to bewail the death of Nadab and Abihu, for "the death of a pious man is greater misfortune to Israel than the Temple's burning to ashes,"  - Aaron and his sons, on the other hand, were permitted to take no share in the mourning, and Moses bade them eat of the parts of the offering due them, as if nothing had happened. Now when Moses saw that Aaron had burnt to ashes one of the three sin offerings that were offered on that day, without himself or his sons having partaken of it, his wrath was kindled against his brother, but in consideration of Aaron's age and his office Moses addressed his violent words not to Aaron himself, but to his sons. He reproached them with having offended against God's commandment in burning one sin offering and eating of the other two. He asked them, besides, if they were not wise enough to profit by the example of their deceased brothers, who paid for their arbitrary actions with their lives, particularly since they also had been doomed to death, and owed their lived only to his prayer, which had power to preserve for their father half the number of sons. Moses' reproof, however, was unjustified, for Aaron and his sons had done what the statutes required, but Moses had on this occasion, as on two others, owing to his wrath, forgotten the laws which he himself had taught Israel. Hence Aaron opposed him decidedly and pointed out his error to him. Moses, far from taking Aaron's reprimand amiss, caused a herald to make an announcement throughout the camp: "I have falsely interpreted the law, and Aaron, my brother, has corrected me. Eleazar and Ithaman also knew the law, but were silent out of consideration for me." As a reward for their considerateness, God thereupon revealed important laws to Moses with a special injunction to tell them to Aaron as well as to Eleazar and Ithamar.