Nadab and Abihu's sin was especially severe because of who they were as the sons of Aaron the high priest, where they went by entering the Lord's presence in the tabernacle, and what they did by burning strange fire before God in disobedience. Their sin was further exacerbated by how they acted with disrespect and likely under the influence of alcohol. Their presumptuous sin was a far cry from momentary failings and showed a lack of sincerity and yielding to God.