Nadav and Avihu, believing that they were taking a step further in giving thanks to God, performed an act of devotion that exceeded the bounds of what is permitted. For this reason, they were punished (Lev. 10, 1-2). Fanaticism, as Shaftesbury already pointed out three centuries ago, is never the way to declare oneself as more pious, it is a gesture that only expresses the intention of dictating new rules. It is not driven by faith, but only for the purpose of domination.
*David Bidussa is an historian.