Then the Lord spoke to Aaron, saying: “Do not drink wine or intoxicating drink, you, nor your sons with you, when you go into the tabernacle of meeting, lest you die. It shall be a statute forever throughout your generations, that you may distinguish between holy and unholy, and between unclean and clean, and that you may teach the children of Israel all the statutes which the Lord has spoken to them by the hand of Moses.” (Leviticus 10:8-11)
Could it be that Nadab and Abihu were drunk and this was another reason they were killed?
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