These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
If I told you that a Christian novelist wrote a book about Adam and Evein space, and that after the plot is resolved he devotes a whole chapter to the characters having a church service where they praise God, many of you would vomit. If I told you the chapter where they sang praises was the best chapter, you might be polite, but in your heart you’d question my literary judgment. But it’s the truth.
The Un-man, aka the Bent One and Satan. It is a being so evil that even to look at its face can cause an unprepared human to pass out, and while it is a highly intelligent tempter with solar system spanning plans, it derives at least as much pleasure from torturing animal life to death.
The transhumanist psychologist, Dr. Frost, in That Hideous Strength.
The detailed description of the head and the creepy paintings in That Hideous Strength. Also Dr. Frost's POV segments.
Older Than They Think: That Hideous Strength addresses the issue of transhumanism and many of its implications. Its first printing was in 1945.
Seinfeld Is Unfunny: At the time the trilogy was first published, most aliens in SF stories were hostile savages intent on destroying humanity. For Lewis's aliens to be morally superior to man was a radical departure... which was widely adopted by later writers, somewhat diluting its impact today. Though, the thing that remains the most original with Lewis' premise is that nearly any other time aliens are morally superior, they tend to not believe in any Deity.
Values Dissonance: You're in a theological debate. You find yourself losing the argument and fear that your audience might be swayed towards the opinions of your opponent. What do you do? If you're Ransom, you give up arguing the point and just kill the dirty satanic villain with your bare hands.
Ransom himself thought that particular solution seemed crass, until he realized that his opponent was playing similarly dirty. The Un-man was using manipulative rhetoric to make his point, and was abusing the fact that he didn't need to sleep in order to physically wear down his opposition.
You must also take into account that A) Ransom's opponent was literally Satan. There was no possible meeting of the minds or compromise here. It was victory and life or defeat and death (of an entire world). And B) This was not his first solution, but his last. He came to this conclusion only after being dragged through weeks of argument. It also required tremendous courage. Ransom fully expected to die, as he was a mortal entering physical combat with a demon. He quickly discovered, to his relief, that it was, physically, one middle-aged scholar against another. And Ransom was a trained boxer.