In Leviticus chapter ten, verse nine, the Lord speaks to Aaron about not drinking wine or strong drinks. Abstinence from intoxicating wine was required of all priests when performing priestly duties. The expectation is to be holy vessels before God and soberly teach the ways of God. The violation of this ordinance about abstinence is severe enough to incur the death penalty in those Old Testament days.
The law imparted after the wrong gesture from Nadab and Abihu caused some to speculate that they were drunk with wine or strong drink when they offered strange fire. Indeed, it is hard to account for any other foot that they should do it. However, having feasted that day upon the peace offerings and drank freely, being the first day of the entrance of their office, they were, it may be supposed, joyful and merry. Presumably, Nadab and Abihu drank more than they should. Therefore this law was essential to restrain such a disorderly and scandalous practice. Not only wine, which is inebriating but strong drinks also is forbidden. If the priest enters the tabernacle, he is guilty.
Nadab and Abihu might drink wine at other times in a calm manner. They were not to drink when they were about to go to service or enter the tabernacle to do it. Indeed, according to Jewish law, a priest, if he drinks wine, is forbidden to enter the tabernacle, the altar, and the holy place. If he goes in and does service, it is profane, unlawful, and rejected. The priest is guilty of death. Some never drink any wine, and others taste but a little of it. However, it is said to harm the nerves, fill the head, or make it heavy, hinder invention and excite lust. Godly leaders must abstain from wine.