There is more to Leviticus 10 than the death of Nadab and Abihu!  We’re told more so we can place the event in context. It is to our detriment when we ignore this!

After Nadab and Abihu’s relatives are summoned to carry their bodies away, Moses tells Aaron and his remaining sons that they are not to mourn “or you will die and the Lord will be angry with the whole community,” (v.6).  Instead, they are to continue their service at the tabernacle (v. 7).  This reinforces the importance of what they are doing and minimizes the focus on Nadab and Abihu’s actions.  God has manifested His wrath against their sin and they are to uphold His judgment by continuing on.  The sin of the two isn’t to carry the day.  This had to have been an enormously difficult thing for Aaron and his sons to do, but they obeyed.  Something of the same thing happened with the prophet Ezekiel when his wife died and he was told not to mourn (Ezekiel 24:15-18).

Aaron’s explanation in v. 19 is worth noting.  He points out that they have obeyed God in all other things, but in light of what had happened to his sons he was not sure if God would have been pleased by their eating.  Unlike Nadab and Abihu, it wasn’t insensitivity that brought about their actions but sensitivity! Moses (acting as God’s spokesman), accepts their explanation. 

But we shouldn’t miss the point.  They didn’t pay for their omission with their lives because they were good (had honorable motives), because Moses’ initial response seems to indicate God didn’t see things the way they did and He expected them to eat the sacrifice. No, their lives were spared because God is merciful.  On a day of severe judgment there was also mercy.  On a day when callousness toward God was punished, the desire to honor God (though expressed incorrectly), was upheld.