You are to distinguish between the holy and the common, and between the unclean and the clean,
Aaron having been very observant of what God said to him by Moses, now God does him the honour to speak to him immediately (Lev 10:8): The Lord spoke unto Aaron, and the rather because what was now to be said Aaron might perhaps have taken amiss from Moses, as if he had suspected him to have been a gluttonous man and a wine-bibber, so...
Commenting on Leviticus 10:8-11
And that ye may teach the children of Israel all the statutes,.... Laws, precepts, ordinances, moral, ceremonial, and judicial, which was the business of the priests to do, Mal 2:7 but one inebriated with liquor would be incapable of giving instructions about any of those things: which the Lord hath spoken unto them by the hand of Moses: particularly those delivered and recorded in Exo...
That we may put difference between holy and unholy - This is a strong reason why they should drink no inebriating liquor, that their understanding being clear, and their judgment correct, they might be always able to discern between the clean and the unclean, and ever pronounce righteous judgment. Injunctions similar to this were found among the Egyptians, Carthaginians, and Greeks.