Following the punitive war against Midian, Elazar the High Priest taught the soldiers how to kasher the utensils they had captured in the war.
“Elazar the kohen said to the soldiers returning from the campaign: this is the rule that God commanded Moses: ... Whatever was used over fire, must be brought over fire and purged, and then purified with the sprinkling water. However, that which was not used over fire need only be immersed in a mikveh [ritual bath].” (Num. 31:21-23)
Why was it Elazar who taught these laws to the soldiers, and not Moses himself?
The Talmud explains that Moses, in his anger at the soldiers for not conducting the war properly, forgot to instruct them to kasher the Midianite utensils. “Because Moses came to anger, he came to error. Thus, the laws of purifying heathen vessels escaped him” (Rashi 31:21, from the Sifre).
Is there an inner connection between the cause for Moses’ anger and the particular laws that he forgot? Also, what happened during the wars against the Emorite kings Sichon and Og that took place prior to the war against Midian? Why didn’t the soldiers already learn these Halakhic rules in those battles?
There are two stages to purifying utensils. First, any forbidden substances absorbed in the vessel must be removed. “Whatever was used over fire, must be brought over fire and purged.” The second stage is immersion in a mikveh. The waters of the ritual bath purify the vessel, preparing it to enter the domain of Israel. This process is comparable to the immersion of a proselyte, as he leaves the non-Jewish world and joins the people of Israel.
The two stages by which vessels are cleansed and purified, thus enabling them to enter the domain of Israel, parallel the two stages by which the Land of Israel was acquired by the Jewish people.
The first stage in acquiring the land took place in the time of the Avot (Patriarchs). “Rise, walk the Land, through its length and breadth, for I will give it to you” (Gen. 13:17). Why did Abraham, Isaac and Jacob need to walk throughout the land? Their travels throughout the land — building altars, digging wells and raising crops — was analogous to the process of purging the utensil, removing the prohibition absorbed in it.
The second stage of acquiring the Land of Israel was the actual conquest in the time of Joshua. The military conquest parallels the immersion of a utensil in a ritual bath. This act completed the transfer of the land to the Jewish people.
The initial purification process of the Avot explains a rather astonishing Talmudic statement. The Sages wrote that during the seven years of conquering the Land, the Jewish people were permitted to eat pork (Chulin 17a). They were allowed to enjoy all of the spoils from the Canaanite nations — even pig-meat! This was in accordance to God’s promise that “You will have houses filled with all good things that you did not put there” (Deut. 6:11). Why did God permit the Israelites to eat blatantly non-kosher foods? This was only possible because the preparatory actions of the Avot had already cleansed the land of its impurities.
For this reason, there was no need to purify the utensils gained in the wars with Sichon and Og. The lands of the Emorites, across the Jordan, took on the holiness of the Land of Israel (Nachmanides on Num. 31:23).
Why then was it necessary to purify the spoils from the war in Midian? Moses, in fact, mistakenly thought that it was not necessary. Moses viewed the war as “God’s revenge against the Midianites” (Num. 31:3). He saw this war as a conquest, so that the land of Midian would also receive the holiness of the Land of Israel.
God, however, knew that the war would not be waged with absolutely pure motives and actions. In the end, the land of Midian would not be added to the Land of Israel. Therefore, God commanded the soldiers to “take revenge for the Israelites” (Num. 31:2). This would not be a war of reprisal for God, but for the Jewish people.
Now we can understand the connection between Moses’ anger and his mistake. He railed against the generals for keeping alive the women who brought about the unfaithfulness of the people and the resulting plague. Their error meant that the war could no longer be considered a war for “God’s revenge.” Moses’ anger led to his mistake. He forgot that, in the new circumstances, this war was no longer part of the conquest of the Land of Israel. It fell to Elazar to instruct the soldiers that the spoils from Midian would have to be purified.
(Shemuot HaRe’iyah, Matot-Masei 5690/1930)