In what sort of situation might someone ask the question “who are we?” It seems most appropriate in the mouth of someone trying to shape her audience into a more coherent community. It is the sort of rhetorical question a party leader might ask at a party rally. In such situations, it means something like “what unifying ideal can we find to make us less like a mob and more like an army, less like people thrown together by accident and more like people who have united to accomplish a task?”