Returning the captive:[1]
The verse states, “When you go out to war and you capture a captive.” The captive in reference in this verse refers to all of the matters that have been captured by one’s animal soul in order to satiate its lusts and pleasures. These matters enter into captivity within the realms of evil, within the lusts of the animal soul. Upon performing Torah and Mitzvahs, and experiencing the above elevation of the animal soul through the fire of heaven being drawn to consume and elevate it, it releases all of its captives that it took when seeking pleasure from the physical world, and elevates it to heaven and holiness.
[1] Likkutei Torah p. 35a