Interestingly enough the incident of Nadav and Avihu are relevant today. As you may recall, Nadav and Avihu, were the sons of Aron. They were priests entrusted to serve in the Mishkan. The Bible relates to us that they were killed by an act of God for disobeying the instructions of the ritual worship service. The text tells us that they offered an Aish Zarah, a strange or different fire offering that wasn’t part of the prescribed ritual. As a result they were summarily killed.
Apparently there are certain religious norms that we are commanded to follow, and beyond that we shouldn’t wonder. A line in the sand has been drawn and as Jews we are expected to seek out God through those acceptable channels. Going beyond that constitutes an Aish Zarah. But how do we determine whether or not we have crossed the normative line?
The mishichistim, a sub cult of the Chabad Lubavitch may or may not have crossed the line, and are offering an Aish Zarah.