They disobeyed the Lord by buring before him the wrong kind of fire, so the fire burned them up - Leviticus 10:1-2
Aaron's sons were called to priests and were given significant and solemn reponsibility
There was little wiggle room in the regulations governing the Tabernacle and the sacrifices
Nadab and Abihu wiggled too much
The treated God's commands casually and carelessly and cost them everything
Their action cost them the blessings that God wants to generouly give to everyone who will listen to him
How do you regard the Word of God?