Here we'll talk about things that a person cannot do on his own property because we want to make sure that his neighbor doesn't lose out on a benefit that he's supposed to have. Somebody's wall was built near his neighbor's wall, not in the same direction, but let's say at a right angle. Picture an L. A person's own wall is the vertical side of the L, and the horizontal side is his neighbor's wall. So there's a right-angle shape. We said, “You're not allowed to build another wall near it to put up another vertical wall on the other side,” sort of blocking in all the land that your neighbor would own. At that point, you're stopping people from walking in the space between those two parallel walls. Walking on that piece of land would firm up the ground, strengthen it, and provide a greater foundation for the neighbor's wall. So you technically blocked people from walking in that area because of the second parallel wall that you put in the same direction as your neighbor's wall. Therefore, you're blocking off entrance in a way, and people aren't going to walk over there. You're not allowed to do that because you want to allow his wall to become stronger.
The same thing applies to a neighbor's window. You have to respect the window. You have to leave a space of four amot (cubits) above the windows or below them. You also have to have a space of four amot in front of them. You have to give them the ability to see out of the window, and you have to ensure their privacy in their home. The top of the wall you're building over here has to be at least four amot higher or lower than the windows. The wall that you're building has to be higher or lower by four amot from the window so that people won't be able to look into the neighbor's house. The wall also has to be distant from the windows so that they have light entering their home and it isn't blocked. You want to give them the full utility of the window that they built it for.