Chasidut su Deuteronomio 21:10

Deuteronomy 21:10: It appears to me that this [verse] alludes to the war with the yetzer hara. We see that there are people of virtue who wage war with the yetzer hara and [can] win; [however], a few days later, they lose and must wage war again. The truth is that this is a big wonder-- what is this about [what’s the point of this cycle]? We already waged this war and conquered the yetzer hara, and that appears to be sufficient [the war has been won]. Now, the yetzer hara overwhelms again. What will happen to them [the person] in the end [of the struggle]? The Torah hints to this in the verse-- “you go out to war”-- which refers to going out of Gan Eden (Heaven) to the physical world for the purpose of this war [to struggle against the yetzer hara]. This is the reason why it says about Yaakov Avinu that Yaakov sought to live in peace. Hashem told Yaakov Avinu: 'is it enough for tzaddikim to have World To Come and want peace in this world too?' And then He sent the difficulty with Yosef [when he got sold]. This means that Yaakov was preparing his portion for the World To Come [approaching his departure from this world], but it wasn't time for him to leave. Therefore, when he was about to depart, the yetzer hara returned. [If wouldn't return, his struggle with the yetzer hara—a central purpose to his presence in the world— would cease and, consequently,] he would depart. Likewise, during the time of King David, the king’s assistant found a young maiden (Avishag) who would warm King David [when he would sleep]. King David was at a level where he had no desires, no yezter hara, as it says “My heart is empty in me” (the Talmud explains that this refers to his successful removal of his evil inclination). That's the meaning of the story: they covered him with clothing and he was not warm, so they were afraid that he'd pass away. [To prevent that they] gave him the maid so that he'd have to fight a new war with the yezter hara so he'd stay longer in this world. That's the connection between the previous parsha (chapter) and this parsha: the end of the previous parsha is “you should do what's just in the eyes of the Hashem,” which is to “go out to war” (this parsha). The path of the just is to always fight the yezter hara-- that's the avodah. When you will do the just, you will go out to war to fight the yetzer hara.

From the Ba'al Shem Tov - the explanation of "when you go to war against your enemy and you take his captives" (Deut. 21:10) - it is that through the argument of the inclination to evil you can conquer it. Meaning, that if the evil inclination is quick in its work of enticing a person to transgress, in order to do its bidding from the Holy One, as it is explained in the allegory of the prostitute in the Zohar, a person should take this lesson (mussar) to heart, and similarly be quick not to listen to the evil inclination - which is the desire of one's Maker, Blessed! And this is "you take him captive", precisely.