In the middle of Parashat Matot, we read about the Bnei Yisrael’s success in war against the Midyanim. Amongst the spoils of war, Bnei Yisrael captured vessels which had become ritually impure due to contact with a corpse during the war. The vessels had to be purified in order to avoid violating the prohibition of being in contact with ritually impure vessels (BeMidbar 31:20). However, following Moshe’s commandment to Bnei Yisrael to purify the vessels, Elazar HaKohein explains to the army further details regarding the purification process. Rashi (31:22 s.v. Ach Et HaZahav), though, explains that these details are actually describing the process of making vessels Kosher. Elazar, therefore, is commanding Bnei Yisrael to purge all of the captured vessels which were captured during the war because they had been used to cook non-Kosher food, and the flavor of the food seeped into the vessels. Thus, when the vessels were placed into the fire and purged, the non-Kosher flavors in the vessels disappeared.
What seems strange from this story is that Elazar, and not Moshe, teaches this Mitzvah to Bnei Yisrael. Why doesn’t Moshe teach this Mitzvah as he does with every other Mitzvah in the Torah? Rashi (31:21 s.v. VaYomer Elazar HaKohein) provides an answer to this question based on the context of the Perek. Earlier in the Perek, Moshe became infuriated when he was notified that Bnei Yisrael killed all of the Midianite males, but spared the women. Hashem punished Moshe by concealing certain laws from him, causing him to err. As a result, Elazar was forced to tell over this Halachah to Bnei Yisrael. Rashi continues to explain that this is not the first time that Moshe lost knowledge due to anger—such instances occur in Parshiyot Shemini and Chukat as well.
Rashi’s comments seem quite puzzling. Firstly, Rashi explains that Moshe “erred,” but this does not seem to be true. Moshe did not err in teaching Bnei Yisrael a law; rather, he perfectly taught one law, and a separate, additional law was concealed from him. Additionally, why did Rashi wait until the third occasion that Moshe forgot something out of anger to explain the principle that Moshe’s anger leads to the concealment of the laws? The Lubavitcher Rebbe provides an interesting explanation to the given questions.
The prohibition of using vessels that were used for non-Kosher food is a logical law, and Moshe clearly was aware of it. Thus, when Rashi states that the law regarding the purging of the vessels was hidden from him, it means something entirely different. Moshe knew that they had to be cleaned, he just failed to recall the method of removal. Moshe remembered that the vessels had to be sprinkled with water, and he thought that the sprinkling would remove both the impurity of the non-Kosher food and the impurity of the dead corpses of war. However, the purging of the vessels was necessary too.
Moshe’s reasoning is quite logical: since the sprinkling of the water was powerful enough to rid the vessels of the impurity of the dead corpses, it would be able to also rid the vessels of the impurity from the non-Kosher food. However, as Elazar teaches, this is incorrect. When Rashi states that Moshe fell into a state of error, this does not contradict the fact that Moshe merely left out one law. Rather, because Moshe forgot the exact process of making vessels Kosher, he made an erroneous presumption with regards to the sprinkling waters of purification.
To answer the second question, we must analyze the three times when Moshe’s anger caused him to forget a law. These three instances are when Moshe hit the rock in order to receive water for Bnei Yisrael (BeMidbar 20:11), when he got into a dispute with Aharon (VaYikra 10:16), and in our case. There is a fundamental difference between these three cases. When Moshe hit the rock, he made a false presumption that Hashem intended for him to hit the rock based on a previous instance where Hashem commanded him to do so (Shemot 17:6). Furthermore, Moshe and Aharon’s argument in Parashat Shemini is over a subtle difference with regards to the Korban Chatat. The underlying theme in both of these cases is that they had a Torah basis. However, in this case, Moshe made a presumption that had no precedent in the Torah, but rather, something which he himself deemed logical.
From this answer, we see that although Judaism requires us to think logically, there are also laws that we cannot understand. We should not try to explain or justify these laws, but we should have faith in Hashem that everything we do has a purpose and is intended to be for our benefit.