God's holiness requires absolute respect from those who serve him

Leviticus 10:1-20
The death of Nadab an Abihu. Because they took their censers, put fir in them and added incense; and they offered unauthorized fire before the Lord.
Aaron and his sons do not let your fair become unkempt and do not tear our clothes, or your will die and the Lord will be angry with the whole community. Do not leave the entrance to the Tent of Meeting or your will die, because the Lord's anointing oil is on you.
Moses said to Aaron offer grain offering and eat it in a holy place,
The rejoicing short-lived. In no time Aaron's sons Nadab and Abihu are deciding to do things their way; and God meets fire with fire, reducing the preiesthood to three.
Perhaps they were under the influence of drink.
Whatever the reason, God's holiness requires absolute respect from those who serve him. His commands are meant to be obeyed, not tailored to suit anyone's fancy
Uncombed hair and torn clothes are signs of mourning.
God's priests are to avoid the excesses of Canaan, where drunkenness went along with religious rites.
The people's sin-offering should have been eaten by the priests in the sanctuary area as a sign that God accepted the offering - Aaron's excuse is not clear, but Moses accepts it.
Why?
The background of the righteousness is mercy of the Lord.
It is the motion of human being(人情世故), God knows the heart of Aaron.
There is the duty to the Lord, so Aaron have to give up the mourn to his sons, this is the duty before the Lord, there is the blessing under this duty.
How?
God's holiness requires absolute respect from those who serve him. No any excuse or whatever the reason.