God said “Do this” and Aaron’s sons Nadab and Abihu, priests ordained to serve the LORD in the Holy Place, did something else. We don’t know exactly what; we don’t know if it was a mistake, if they just didn’t care, if they were close to being right… but they did not follow the instructions God had given. The people of Israel are about to learn a hard lesson about God being serious about his laws and statutes, especially with the religious leaders who are responsible for his people. Shepherds are held to a higher standard because God loves his sheep.

Leviticus 10

Nadab and Abihu, the sons of Aaron, each took his censer, and put fire in them, and put incense on them, and offered strange fire before the LORD, which he had not commanded.