You are right, the justices have read and analyzed all the briefs and are completely familiar with the argument of both sides. However, oral argument consists mostly of questions from the court to the litigants. You never get more than a few words out before you are interrupted by a question. They come rapid-fire, one after the other. That’s really how you prepare best for oral argument, by anticipating the off-angle questions the court might ask and, preparing good answers that will lead back to your argument.
Thanks. Good points…