That’s typical Modernist language Catherine is using. World War I "blew up" the idea that the world was a safe place, and the Modernists were obsessed with fragments and pieces and breaking in general.
Stretcher bearers came in all the time, put their stretcher down, unloaded them and went away. (9.137)
There is a somber rhythm to Hemingway’s description of this procession of wounded men. And it presents a striking and vivid image of the war.
"And the ones who would not make war? Can they stop it?" "I do not know." (11.53, 54)
This is a rather meta-fictional moment. Hemingway’s novel is often seen as a protest against war, and the sentence expresses doubt over whether such protest can really help stop it.
How many had I killed? I had not killed any but was anxious to please ─ and I said I had killed plenty. (15.2)
This moment is important because later, when Frederic and Aymo shoot the soldier, we know it’s his first time to kill a man.
A British major at the club told me the Italians had lost one hundred and fifty thousand men […] (21.1)
And that’s just Italy, and that’s just in part of the war. Gives you an idea of the scope of the destruction of World War I.
"Miss Van Campen," I said. "Did you ever know a man who tried to disable himself by kicking himself in the scrotum?" (23.27)
This is one of the few times we see Frederic express anger toward another person in the novel. And Frederic surely knows he’s on thin ice with Miss Van Campen. His anger toward her could be seen as a subconscious expression of guilt over his convalescence, and a way to get sent back to the front without having to consciously choose to be away from Catherine.
Abstract words such as glory, honor, courage, or hallow were obscene beside the concrete names of villages […] (27.29)
This comes from one of the novel’s most famous passages. He comes to believe that when villages, and towns, and human lives are destroyed, all the words that are traditionally associated with war and battles become perversions of what they are supposed to mean.
"If there is a retreat, how are the wounded evacuated?"
"They are not. They take as many as they can and leave the rest." (27.45)
This is a chilling moment in the text. We are filled with a deep sadness to think of the wounded men left in the rain to fend for themselves if they can, and most likely to die in great pain, without any knowledge that they are loved, or cared for, or appreciated.
In civilian clothes I felt a masquerader. (34.1)
Frederic was a civilian before he wore the uniform. We wonder if when he first put on a uniform he felt like a masquerader too. Clothing has a fair amount to do with identity in this novel. Think of the German’s helmets, or Catherine’s blue cape.