The tabernacle had just been completed, the priests had been anointed, and the sacrifice had been offered on the altar. Everything had been done as God had commanded when something terrible happened. Two of Aaron's sons, Nadab and Abihu, decided to do something different. They both put incense in their censers and burned strange incense before the Lord. It was not what God had prescribed and the result was tragic. Fire came from before the Lord and consumed both of them immediately (Lev. 10:1-3).
Why did God kill them? The passage gives several possibilities. First, Nadab and Abihu were doing things their own way. Right after their deaths, Moses was quick to point out that the priests were to sanctify and glorify the Lord before the congregation (3). The only way to do this was by following the specific instructions given to them by the Lord. In other words, there was only one way to worship the Lord and that was what God had made known to them.
Second, Nadab and Abihu may have been intoxicated when this happened. The passage doesn't say that this was the reason, but note the admonition of the Lord in verses 8-11. God directly told Aaron that the priests were to have a clear mind when they were fulfilling their duties in the tabernacle. They needed to be able to teach the Israelites what God required for proper worship. And when someone brought an offering, the priest would need to determine if it was acceptable for worship. Alcoholic beverages are known to diminish one's ability to think clearly. This could explain why these two acted as they did.
We may never know exactly why these two were judged by God, but we know unmistakably that He takes these things seriously. Every minister of God would be wise to consider this passage before leading people in worship. God is not interested in "strange" worship which does not recognize his holiness. He wants to be set apart by his people as the holy God that he is. He also wants to be worshiped his way. As Jesus pointed out to the woman at the well, God desires that his people worship him "in spirit and truth." And if that is going to happen, God's people will need a clear-minded teacher who knows the Scriptures and can point out what is acceptable or not acceptable to the Lord.
Let us consider these truths the next time we bring our worship before our holy God.