1 Aaron’s sons Nadab and Abihu took their censers, put fire in them and added incense; and they offered unauthorized fire before the LORD, contrary to his command. 2 So fire came out from the presence of the LORD and consumed them, and they died before the LORD. (New International Version)
As leaders, they had special responsibility to obey God because they were they were in a position where they could easily lead many people astray.
Aaron’s sons were careless about following the laws for sacrifices. In response, God destroyed them with a blast of fire.
Performing that sacrifices were an act of obedience. Doing them correctly showed respect for God.
It is easy for us to grow careless about obeying God. Some of Gods commands are simple to obey.
Others, require more careful attention.
Disobedience to God always brings correction.