Adam Clarke on Leviticus 10:6

Uncover not your heads, etc. - They were to use no sign of grief or mourning,

1. Because those who were employed in the service of the sanctuary should avoid every thing that might incapacitate them for that service; and,

2. Because the crime of their brethren was so highly provoking to God, and so fully merited the punishment which he had inflicted, that their mourning might be considered as accusing the Divine justice of undue severity.