1. Nadab and Abihu are two of the four sons of Aaron, the older brother of Moses, and they play a significant role in the book of Leviticus in the Bible. The story of Nadab and Abihu is found in Leviticus 10:1-3.

2. In this story, Nadab and Abihu were serving as priests in the newly established Tabernacle, and they offered what the Bible describes as "unauthorized fire" before the Lord. This act was seen as a violation of God's commandments, and as a result, fire came out from the presence of the Lord and consumed them, killing them instantly.

3. The exact nature of their offense is not entirely clear, but it is believed that they may have used incense or fire that was not taken from the altar of burnt offering, which was the only place where fire was to be obtained for use in the Tabernacle. This act of disobedience was seen as a serious breach of protocol and respect for the holiness of the Tabernacle and its rituals.

4. The story of Nadab and Abihu serves as a cautionary tale about the importance of following God's commands and respecting the sanctity of religious rituals. It also highlights the gravity of sin and disobedience in the eyes of God and underscores the seriousness with which God regards His own holiness.