The Torah in Parashat Shemini tells the tragic story of Nadab and Abihu – two of Aharon's sons, who perished on the very first day they began serving as Kohanim in the Mishkan. After a special series of sacrifices were offered, with Aharon's sons performing the service for the first time, a fire descended from the heavens onto the altar and consumed the sacrifices, signalling the arrival of the Shechina (divine presence) into the Mishkan. Thereafter, Nadab and Abihu brought an incense offering, whereupon a fire came and consumed them. Rashi (10:2) brings different opinions as to the precise sin committed by Aharon's sons. One view – which appears in the Gemara (Erubin 63a) – is that of Rabbi Eliezer, who explains that "Horu Halacha Bi'fneh Moshe Rabban" – Nadab and Abihu were guilty of determining the Halacha without consulting with their Rabbi, Moshe. They reasoned that although a supernatural fire came down onto the altar from the heavens, there was nevertheless a requirement for the Kohanim to kindle a fire of their own on the altar, and this is the reason why they brought their offering. In truth, this conclusion was correct; there was, in fact, such a requirement. Nevertheless, Nadab and Abihu committed a grave offense by acting independently on their line of reasoning without first receiving guidance from Moshe. In Moshe's presence, they did not have the authority to establish Halachic norms on their own. Therefore, although their reasoning was entirely correct, they were guilty of a grievous sin in that they did not submit to Moshe Rabbenu's authority. The Lebush Ha'ora (Rav Mordechai Yoffe, c. 1530-1612) noted that Rabbi Eliezer's understanding of this episode is rooted in a careful reading of the text. In telling of Nadab and Abihu's offering, the Torah writes that they offered an "Esh Zara Asher Lo Siva Otam" – "a foreign fire which He did not command them." If the problem with the Nadab and Abihu's act was the offering itself, then the Torah should have simply stated that they brought an "Esh Zara" – an offering that was foreign, that was unwarranted and hence forbidden. But the Torah added "Asher Lo Siva Otam" – that Nadab and Abihu did not receive the command to bring this offering, suggesting that this was the essence of their sin. Hashem had taught Moshe the rule that the Kohanim were to produce their own fire on the altar, but this information had not yet been communicated to Aharon's sons. Moshe had been commanded to place fire on the altar – but Nadab and Abihu's hadn't. And thus the Torah emphasizes that this was an offering about which Moshe was commanded, but they weren't – and they were therefore punished for acting independently. This tragedy presents us with a crucial lesson in humility. Namely, even when we are confident that we are correct, we must still consult with those wiser and more knowledgeable than us. We must have the humility to recognize our limits, to realize that even things which seem obvious and intuitive to us might not necessarily be correct. We need to acknowledge that there are people with greater knowledge and wisdom whose advice is valuable and even indispensable. We should never feel too confident to ask, to seek guidance, to double check, to consult, to request advice. Even when we are certain, we must humbly question our conclusion and receive instruction and insight from those who know more than we do.