Aaron’s two oldest sons, Nadav and Avihu, are incinerated because they light the altar with unauthorized fire (Leviticus 10:1-2). However, as RaShI’s grandson, Rabbi Samuel ben Meir, points out, lighting the altar is exactly what was expected of them every day! As the Torah states: “The sons of Aaron the priest shall put fire upon the altar and lay wood in order upon the fire” (Leviticus 1:7). So why should these two be punished with death while performing what they are commanded to do?
RaShBaM explains as follows: “On the day of the inauguration of the priests in divine service God did not command that they light, neither did Moses want the altar ignited by human means since all were anticipating the descent of fire from above to sanctify God’s name and allow all to know this was heavenly fire.” Just as Elijah the prophet who challenged the priests of Ba’al at Mount Carmel (1 Kings 18:25), the igniting of the altar by divine fire was essential to establish publicly the investment of God in Israelite practice.
The terrible mistake Nadav and Avihu make is in failing to be aware of the moment. It is a common mistake, too. Jewish law, for example, has much to say about what a worshipper should do when the worshipper recites the usual daily prayers only to remember later on that the day was the New Month and a special prayer was required. Sometimes worshippers become so accustomed to routinely say the same words that worshippers forget the moment. The difference, however, is that the penalty for reciting the wrong prayer is to repeat the proper prayer. The penalty for Nadav and Avihu was death.
Perhaps the way to look at this sad episode is that the moment of mindlessness in the case of Nadav and Avihu had extraordinary implications. Repeating the proper prayer affects only the worshipper. But the igniting of the altar deprived all Israel of beholding the confirmation that it is God who sanctions the sacrificial cult and all of Israelite service. That was an error of supreme consequence.