The quiet allegory of racism
The most racist part of the story that Father Desbois hears is that Nazis didn't attempt to learn the names of the victims they executed throughout Eastern Europe if they looked Romany or Jewish. But that doesn't mean that the Nazis were the only racists in the story. Because racism against Romany and Jewish people was prevalent at the time, many people still don't know anything about what the Nazis did to those populations in Eastern Europe, because the deaths were not viewed as newsworthy.
Nazis as archetypes of evil
This book portrays Nazis correctly as the arbiters of evil. The priest is a representative of his religious views, and the Nazis are in his mind the most heinous kind of evil. They murdered innocent people as if they were hunting animals, never caring about the victims or their families, and burying them haphazardly in mass graves. The Holocaust of Western Europe is well-known, but this is another aspect of that same story that often gets neglected.
Empathy through painful motif
The novel is about more than history, though. For instance, Father Desbois is giving a demonstration of empathy that is worthy of notice. To him, ministry is to share in the sufferings of other people. His holy task from God is to practice empathy well, and he does this by letting people vent their tragic stories, by listening, by sympathizing with their deep suffering, without aversion. He doesn't shy away from painful stories. This is a proper depiction of empathy through motif, and it is shown as a sacrifice, because it is hard for him to bear the weight of this knowledge.
The human experience and suffering
Because he is a priest, and because he is dealing with one of the most tragic moments of human history, the memoir takes on a tone of existential dilemma. His crisis is to find meaning in the suffering that humans endure. He sees the senselessness of war, but that doesn't take away from the real damage and felt suffering that people have endured. The whole nation is damaged, and he can barely fathom the entirety of that suffering, let alone reconcile it to his religious beliefs.
Death rites
To the priest, the absence of death rites is an abominable evil. He sees that the Nazis cared less about the human lives they took than they would an animal. The burials given for the dead were typically mass burials, and they rarely listed names. The rites symbolize the value of human life and the respect for the dead, but these Nazis were specifically disrespectful of these dead bodies. They mistreated the corpses and stopped people from collecting them for proper burial. To the priest, this symbolizes true evil, because they are defiling the spiritual worth of their victims.
