It strikes me that he was, cynically, being told that he should be less gung-ho; not believe his own rousing speeches. "You listen to yourself too much, mate!"

He was, we are told, a staff officer, not a front line officer leading the men. Part of his role would be to persuade others into danger, pour la gl˘ire de la patrie, not to put himself at risk and become injured to the point where he was no longer of use. Without knowing more about this officer it is difficult to guess exactly what was meant, but this idea certainly appeals to me and makes sense of the apparently unnecessarily callous comment. It provides 'the something missing' that Dr Bill senses.