Leviticus 10:1 And Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it, and put incense on it, and offered strange fire before YHWH, which He had not commanded them.
Leviticus 10:16-20 And Moses carefully looked for the goat of the sin offering. And behold, it was burned! And he was angry with Eleazar and Ithamar, the sons of Aaron left alive, saying, (17) Why have you not eaten the sin offering in the holy place, since it is most holy, and He has given it to you to bear the iniquity of the congregation, to make atonement for them before Jehovah? (18) Behold! The blood of it was not brought within the holy place! You should indeed have eaten it in the sanctuary, as I commanded. (19) And Aaron said to Moses, Behold, this day they have offered their sin offering and their burnt offering before YHWH. And such things have happened to me. And if I had eaten the sin offering today, should it have been accepted in the sight of YHWH? (20) And Moses heard, and it was good in his eyes.
Aaron’s sons, Nadab and Abihu, spontaneously worshiped God by offering incense, and they were destroyed for it. Aaron disobeyed God by not precisely following the rules of the sin offering. Nadab and Abihu were destroyed, while Aaron was justified. God appears to have acted arbitrarily and unfairly.
This appearance is due to our limited vision. God sees through us. He knows us all the way down to the heart and bone. Nadab and Abihu were not destroyed for an act of spontaneous worship. They were destroyed for acting presumptuously. They said in their hearts, “We know what God really wants. We can improve on the worship he commanded.” Aaron was not destroyed, despite his disobedience, because he said in his heart, “I am full of sorrow and anger and am not able to atone for the sins of the people with such sin in my heart.” Instead of eating some of the sacrifice and using the blood to atone for Israel, he burned it all, sending everything directly to God. Although he was disobedient, he acted out of humility and reverence, while his sons acted out of pride.