That's like saying the purpose of a blade is to cut, which while true, is a fairly useless statement. A blade may be an artisan's tool, or a soldier's weapon, o

That's like saying the purpose of a blade is to cut, which while true, is a fairly useless statement. A blade may be an artisan's tool, or a soldier's weapon, or something you use to cut your food. All cutting implements but with quite different applications and functions. So the question regarding the wall's function is what was it a barrier against? When we build houses, we put holes in the walls so that they are less of a barrier to people, yet remain an effective barrier against the external environment. Other walls are meant to be barriers to specific animals, yet completely permeable to others.