Salam alaikum Mia,
This is just me taking a stab at it, I'm not completely sure. It seems that this verse is saying taking of war captives is only permissble if you're in a situation where you have to in other words, a conflict. A defensive conflict where you have no choice. You can't just go out and get yourself some captives, because you want yourself some "commodities" (sell some slaves?), so don't go invading people so you can be rich. Remember the hereafter. That's my best guess. Not sure what the context is because I havent read the whole chapter or surrounding verses.
By the way I am in no way an Arabic language expert, but my basic knowledge in Islam tells me that the Sahih International translation is absolutely atrocious. We can't transgress bounds, nor harm a people that never harmed us, so "infllicting a massacre" is a very terrible choice of words that violates other parts of the Quran. Not sure about the free-minds one though.