Nadab and Abihu served as priests under their father, Aaron. They too had seen the Lord (Exodus 24:1, 9-10). They too had received very specific laws for worship. They did not lack knowledge; they lacked submission.
Now Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it and laid incense on it and offered unauthorized fire before the LORD, which He had not commanded them. And fire came out from before the LORD and consumed them, and they died before the LORD (Leviticus 10:1-2).
Do men engage in “unauthorized” acts because they plan to be punished? Evidently, these priests thought they could get away with burning incense their own way. Whatever they believed, did their faith, based on first-hand experience with God, save them? God turned Aaron’s two sons into a fiery example with a lesson: “Among those who are near Me I will be sanctified, and before all the people I will be glorified” (Leviticus 10:3). Experiential knowledge does not glorify God. Turning that knowledge into obedience honors God!