Why do you think the author has included a scene where his friend Mittelstaedt is now the commander over his former schoolmaster?

Mittelstaedt, a former classmate of Paul's in nearby barracks, tells him that Kantorek has been called into the war in a low rank. Mittlestaedt tells Paul how he lords his authority over their former teacher. He takes him to the parade ground. Paul almost laughs when he sees Kantorek decked out in ill-fitting military uniform. Mittlestaedt torments Kantorek in the exercises, even quoting patriotic words Kantorek himself used to preach. Certainly the illusion of valor in war was grinded into Paul and his friends by authority figures like Kantorek. These people had little idea of the Hell that they were sending the boys to. Now their schoolmaster Kantorek gets to see first hand the realities of war rather than lies of grandeur that he was telling his students.