Up until now, everything has been done according to the Lord’s commandments:
The Lord had given Moses a detailed description of the tabernacle and everything in it (Exodus 25:1 – 30:38). Consequently, the tabernacle had been made exactly according to these instructions, to the point that the description of the making of the tabernacle sounds like an echo of the instructions (Exodus 35:1 – 40:38).
The consecration of Aaron and his sons echoes the instructions in Exodus 29:1–46. Again and again, Leviticus 8:1–36 emphasizes that it was done in the way as the Lord had commanded it.
This also applies to Aaron’s first offering (Leviticus 9:1–24).
So, what Nadab and Abihu did was in sharp contrast to everything that had been done up till now.
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.