“God spoke to Moses saying: Command Aaron and his sons”
~ Leviticus 6:1-2
The majority of mitzvot are communicated using the verb “say” or “speak”. However, here the Torah uses the more emphatic “command”.
These laws pertain specifically to the priests who serve in the Temple as representatives of the entire nation. Like all civil servants, this meant long hours, basic pay and not much appreciation.
With such difficult conditions, even the inspiration of their Holy work would wear off. Speaking wouldn’t suffice. Instead they needed something more enduring – a commandment.