Although the Kaiser's visit to the front is meant to inspire the men, to get them pumped up for the war, it really has the opposite effect on Paul and his comrades. It makes them question the war completely.
They get new clothes for the Kaiser's visit and then those are taken away. The Kaiser is not an impressive man. Both of these disillusion them.
After his visit, they talk about how pointless the war is. They say that war only exists to benefit the powerful people --- to let the leaders do something that will get them into the history books. They wish that these leaders would just fight it out among themselves.