The doctor's letters are no doubt an immensely valuable resource concerning history of WWII and the holocaust. More importantly, it's a record of human reaction to the horrors of what he observed, and very likely provides insight into experience that transforms a person so adversely.
Nowadays we call it PTSD and of course it's still a scourge in a world filled with horrific conflict. Perhaps these letters would encourage people suffering in the way the doctor knew to get treatment, above all talk about it, hard as that is to do.
I hope the letters are donated to a proper archive for preservation and made accessible so that the lessons contained can be widely shared, and become an encouragement to healing.