In order to understand the phrase “strange fire,” we must review the story in Leviticus in which it appears. The first tabernacle had been erected, and Aaron was doing a lot of sacrificing per God’s instructions (Leviticus 8—9). One day, two of Aaron’s sons, Nadab and Abihu, came along and offered incense with “strange fire.” The Hebrew word translated “strange” means “unauthorized, foreign, or profane.” God not only rejected their sacrifice; He found it so offensive that He consumed the two men with fire.
After Nadab and Abihu were killed, Moses explained to Aaron why God had done such a harsh thing: “This is what the LORD spoke of when he said: ‘Among those who approach me I will show myself holy; in the sight of all the people I will be honored’” (Leviticus 10:3). The exact nature of the profane fire isn’t known, but, since it was the fire that was unauthorized, it could be that Nadab and Abihu were burning the incense with fire of their own making rather than taking fire from the altar, as specified in Leviticus 16:12. Or it could have been that the two men came into the tabernacle drunk and therefore could not remember what was a violation and what was not (Leviticus 10:8–9). Whatever it was the men did to render the offering profane, it was a sign of their disregard for the utter holiness of God and the need to honor and obey Him in solemn and holy fear. Their carelessness and irreverence were their downfall.
In judging Nadab and Abihu for their strange fire, God was making a point to all the other priests who would serve in His tabernacle—and later, in His temple—and to us, as well. Since this was the first time sacrifices were being offered on the altar and Israel was getting to know the living God better, when Aaron’s sons were disobedient and profane, God displayed His displeasure in no uncertain terms. God was not going to allow the disobedience of Aaron’s sons to set a precedent for future disregard of His Law. A similar story occurs in Acts 5:1–11, during the time of the early church. A husband and wife lie to Peter about some land given to the church, and they are judged with physical death because of their lie. As Peter puts it, “You have not lied just to human beings but to God” (Acts 5:4).
God knows our hearts. He knows what we truly believe and our attitude toward Him. We cannot offer to Him proud “sacrifices” that are unworthy of Him. He seeks those who come to Him in humility, ready to sacrifice their pride and lay before Him humble and contrite hearts grieving for sin (Psalm 51:17). Certainly, there is grace and forgiveness and plenty of “second chances” for those who belong to Him. But God wants us to know that He is serious when it comes to His honor and glory. If there is willful disobedience in the life of a believer, then God disciplines us out of His great love for us (Hebrews 12:7–11). If such disobedience continues, God will take harsher measures until we understand how we are disappointing Him. If we continue in our disobedience even after that, then God has every right to remove us from this earth (see 1 Corinthians 11:29–30).