1. Leviticus 10:9 (ESV)
  2. Exposition

Why is there a prohibiting of alcoholic beverages in this context?

Leviticus 10:9 (ESV)

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.

It is sometimes assumed that Nadab and Abihu had been drunk when they committed their offence. However, this is not implied. This prohibition may have been included as a warning only.