The commandment of abstinence applies to the priests only during their times of service. They must be sober, self-controlled, and composed, so that they can be accurate and careful in performing the rituals assigned to them. They were also supposed to teach the people. When a layman would bring an offering and turn to a priest to perform it for him, the priest would give directions and explanations (see, e.g., Haggai 2:11–13). Thus, the priest has to be able to distinguish clearly and speak intelligibly.
9 “Drink no wine or strong drink, you or your sons with you, when you go into the tent of meeting, lest you die. It shall be a statute forever throughout your generations.