If someone owes us an unpaid debt, we can't just go into their house and seize property. This can only be done by going to beis din and, if they so order, they will send an agent legally empowered to take care of things. Not only may we not go into the borrower's house, we likewise may not accost him in the street.
The reason for this mitzvah is that we're not animals and we don't live in a state of anarchy. To allow people to go around seizing property at their own discretion fosters an attitude of "might makes right" and it enables the strong to get their way through bullying and intimidation. Instead, the Torah only allows property to be confiscated by the courts according to the rules of who is right and who is wrong. This encourages a just society.
This mitzvah applies to both men and women in all times and places. This mitzvah is a "lav she'nitak l'asei," a prohibition that, if violated, causes a positive mitzvah to kick in. Specifically, one should not seize property but if he does, Mitzvah #587 tells us that it must be returned. This mitzvah is discussed in the Talmud in tractate Baba Metzia (113a-b) and codified in the Shulchan Aruch in Choshen Mishpat 97. This mitzvah is #239 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #59 of the 194 negative mitzvos that can be observed today as listed in the Chofetz Chaim’s Sefer HaMitzvos HaKatzar.