The language used in the dialogue is quaint using "thou" instead of "you".   It could be that the Spanish counterpart of the use of "tu" instead of "vous" in French used as a term of endearment.   It seems to have been part of the language of the Spanish Republic which also used "comrade" as in the Soviet Union.

The description of the battle scenes were interesting except that I had to read three hundred pages of not so interesting stuff to get to them.  It is the story of an American volunteer who is sent to join a band of Loyalists in the hills and to blow up a bridge. 

The author also writes of the atrocities committed on both sides.  Air power features prominently.  I guess that it was in the Spanish Civil War that for the first time the civilian population was bombed in their own homes by the same German bombers that would bomb London a few years later.

The Spanish Civil War was the first confrontation between the forces of Fascism
and the forces of Socialism.  It was the first opportunity to check the spread of Fascism. However, the changes brought about by the Spanish Republic were equally as abrupt as the change brought by Fascism.

It has intrigued me that France's refusal of any assistance to the Spanish Republic led to the fall of the Spanish Republic to the Fascist dictatorship which, in turn, assisted Hitler in his invasion of France in 1940.

Getting back to Hemingway's novel, I guess its reputation preceded it.  At least, the ending was unpredictable.  It did not end as I expected.