Just putting in 2 quotes that stuck out to me.
In regards to Christmas:
...the prisoner unconsciously felt that by observing the holiday he was as if in contact with the whole world, that he was therefore not entirely an outcast, a lost man, a cut-off slice, that things in prison were the same as among other people.
It is rather eye opening to realize that the "gentlemen" class barely saw those below them as human and it wasn't until in prison himself that D began to articulate such ideas.
In regards to prison authorities:
"The law says so; what more do you want?" they say, and are sincerely surprised that, in addition to the law, sound reasoning and a sober mind are also required of them.
When "Law" becomes its own reason for existence, it becomes empty and meaningless. It becomes "Rules". And as terrible as mankind is at obey the Law, they are even worse at obeying Rules.
I am also currently reading I am a Cat by Sōseki Natsume and both of these books are written in that journal'y style. I have to be honest, it is a bit much. While one is Russian and the other Japanese, the style is the same. It gets rather boring.