Throughout Leviticus 8:1 – 9:24 the phrase, “Just as the Lord had commanded” emphasized the obedience required by the priesthood. Now the reader is told that Nadab and Abihu did that, “which he had not commanded them.” Nadab and Abihu drew near to God in a disrespectful manner, one that is not in accordance with his Word. It is, therefore, a deliberate disobedience.
1 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.