According to the Rambam, the war against Midian also had the status of conquest, even though its main purpose was vengeance. According to Rabbi Akiva, the rule that Shevet Levi does not go out to war applies only with regard to Eretz Yisroel, since they were not given an inheritance in Eretz Yisroel. However, wars outside Eretz Yisroel, whose purpose is to expand the borders of Israel and increase the fame of the king — which reflects the greatness and fame of Hashem — and similarly the war against Midian, whose purpose was vengeance for Hashem, do apply to Shevet Levi, whose role is to be the army of Hashem.
The war against Midian was not for the sake of conquest, but for the sake of vengeance. Based on this, we can explain the Raavad’s question on the Rambam. The Rambam writes that the warning to Shevet Levi not to take a share in the spoils applies only “in the land concerning which a covenant was made with Avraham, Yitzchak, and Yaakov, which their descendants inherited and divided among themselves. But in all other lands… the Kohanim and Leviim are like all other Jews in those lands and in their spoils.” The Raavad asks: “But in the spoils of Midian, they did not take a share with Israel, except through the terumah and by the command of the Creator of all, blessed be He.” The explanation may be that one cannot raise a question from the war against Midian, because the war against Midian was not like other wars. Other wars are defined as conquest, whereas the war against Midian was defined as vengeance.
However, it must be added that since the Rambam rules that when besieging a city, it should be surrounded only on three sides, “as it says, ‘They waged war against Midian…,’” this implies that he holds that the war against Midian is connected to, and shares the same category as, other wars. Therefore, we must say that according to the Rambam, there was also an element of conquest in the war against Midian, even though its primary purpose was vengeance, as explained above.
The idea is as follows: In the war against Midian, we find that according to Rabbi Akiva, Shevet Levi was also included in the command, “From each of the tribes of Israel you shall send to the army.” Although in general Shevet Levi was set apart to serve Hashem and minister before Him, and therefore they do not go out to war, this applies specifically regarding the land given to Avraham, Yitzchak, and Yaakov, which was given to the Jewish people as an inheritance. Shevet Levi has no portion in that, because they were separated from worldly pursuits. But wars outside Eretz Yisroel, whose purpose is to expand the borders of Israel and increase the fame of the king — which reflects the greatness and fame of Hashem — and similarly the war against Midian, whose purpose was vengeance for Hashem, do apply to Shevet Levi, whose purpose is to be the army of Hashem.
The lesson in a person’s Divine service is that even someone whose spirit moves him to be like Shevet Levi cannot say that he has no connection with the world. Rather, he must involve himself in the vengeance of Hashem against Midian: to overcome and nullify those matters that oppose Hashem. In personal service, this means nullifying baseless hatred among Jews and working to bring about love and unity among the Jewish people.