In the Book of Exodus, the Book of Leviticus and the Book of Numbers

Book of Numbers

The Book of Numbers is the fourth book of the Hebrew Bible, and the fourth of five books of the Jewish Torah/Pentateuch....

, Nadab  and Abihu were respectively the eldest and second-eldest of the sons of Aaron

Aaron

In the Hebrew Bible and the Qur'an, Aaron : Ααρών ), who is often called "'Aaron the Priest"' and once Aaron the Levite , was the older brother of Moses, and a prophet of God. He represented the priestly functions of his tribe, becoming the first High Priest of the Israelites...

. They offered a sacrifice with unauthorized fire before the LORD

Yahweh

Yahweh is the name of God in the Bible, the God of Abraham, Isaac, Jacob, Jews and Christians.The word Yahweh is a modern scholarly convention for the Hebrew , transcribed into Roman letters as YHWH and known as the Tetragrammaton, for which the original pronunciation is unknown...

, disobeying his instructions. Nadab and Abihu were consumed immediately by God’s fire. They trespassed upon a task that belonged only between God and the high priest. The priests were commanded not to mourn, but the people at large were permitted.

Background

Nadab and Abihu were the first two sons of Aaron the Levite

Aaron

In the Hebrew Bible and the Qur'an, Aaron : Ααρών ), who is often called "'Aaron the Priest"' and once Aaron the Levite , was the older brother of Moses, and a prophet of God. He represented the priestly functions of his tribe, becoming the first High Priest of the Israelites...

 by his marriage to Elisheba. He had four sons in total, the younger two sons being named Eleazar and Ithamar. According to the book of Exodus, Aaron and his sons were the first priests appointed as the priestly system was established by God. The Levites as a tribe were later ordained for the priestly service after answering a call to take the LORD’s side after the idolatry centered around the golden calf

Golden calf

According to the Hebrew Bible, the golden calf was an idol made by Aaron to satisfy the Israelites during Moses' absence, when he went up to Mount Sinai...

. After the death of Nadab and Abihu, Eleazar and Ithamar took their places as priests, because neither Nadab nor Abihu had any sons.

Violation of God’s law and punishment

In Leviticus 9 and Exodus 30, God outlines a proper sacrifice to him. Aaron, the chief priest, was to present all offerings representing himself and the people. God would send his own fire to consume the sacrifice as a sign of his presence.

When Nadab and Abihu lit the offering in the censers themselves, the fire was unauthorized and God was not in it. They prepared an incense offering upon kindling of their own. No offering of incense had been ordered; the only legitimate incense offerings were those made daily by the high priest upon the sacred altar. Aaron’s sons neglected the command to wait for holy fire and offered incense with unauthorized fire. Anyone who altered the sacrificial system assumed a prerogative belonging to God alone. God determines the judgments that are carried out against those who either add to or take away from the declarations of God.

Burial

After the death of Nadab and Abihu, Moses dictated what was to be done with their bodies. He told Mishael and Elzaphan, the sons of Aaron’s uncle, to carry the bodies away from the sanctuary to a place outside of the camp. He specified for Mishael and Elzaphan to be careful to only touch Nadab and Abihu’s tunics, and not their bodies. The first concerns in burial were to prevent what is holy from being defiled and the service of God from being disrupted. The corpses had to be removed immediately, because to allow the uncleanliness of the bodies to remain in the sanctuary could invoke God’s wrath again. The bodies were lifted up “by their tunics” to avoid direct physical contact, preventing the carriers from becoming unclean as well.

Mourning

Aaron and the other surviving priests are commanded not to mourn, participate in mourning rituals, or have contact with the dead. This was applicable not only in this case, but it was an ongoing command; these things are were generally forbidden to priests. Priests were to avoid everything that might disqualify them for God’s service.

The command not to mourn also applied because the crime of Nadab and Abihu was so provoking to God and fully merited the punishment which God had inflicted. To mourn in this case could be seen by the people as accusing God of undue severity. Both the people and the priests needed to show submission to a righteous judgement. If the anointed priests were to sin in this manner, the blame would fall not only upon them but also upon the people.

However, the people in the community as a whole were allowed to mourn and display grief. The death of Nadab and Abihu was tragic yet deserved, and the people were to first recognize that it was deserved and then mourn their death.

Catholic view

Whether Nadab and Abihu neglected to follow God’s outlined sacrificial system out of presumptuousness, or out of thoughtlessness and inattention, their fault was severely punished so that all might learn to comply exactly with God's commands, and not try to change them or explain them away. The mixing of falsehood with the word of God was a serious sin. Those in power, like priests, should be especially careful in their behavior, because they are examples to those they serve.

Reformation and Post Reformation view

Nadab and Abihu were in a great position to become honorable and respected priests. If Nadab and Abihu’s deed had been done through ignorance, they may have been allowed to bring a sin-offering. But instead they did it presumptuously, and in contempt of God's majesty and justice. They were therefore cut off, for the wages of sin is death. The sin and punishment of these priests showed the imperfection of that priesthood from the very beginning, and that it could not shelter any from the fire of God's wrath.

View in Judaism

Nadab and Abihu’s sin was an encroachment on duties which devolved on their father alone as the high priest. But the offense was of a far more aggravated nature than an encroachment on duties. There were multiple sins contained in one act. First, they ventured unauthorized to perform the incense service—the highest and most solemn of the priestly duties. They also engaged together in a work which was the duty only of one. And, thirdly, they presumed to light the fire on the offering themselves. In this respect, "they offered strange fire before the Lord"; they were guilty of a presumptuous and unwarranted intrusion into a sacred office which did not belong to them. In these actions they showed carelessness, irreverence, and a want of faith, lamentable especially for those in the priestly service. A precedent of such evil tendency was dangerous, and it was imperatively necessary, therefore, as well for the priests themselves as well as for the sacred things, that God should give a punishment.