I finished reading this Ernest Hemingway novel a few days ago, so I've been able to reflect on what I feel about it. Initially I read it as a teenager, but I don't remember exactly how I reacted to it then.
Spoiler alert: If anyone reading this thinks they may someday read this book and if knowing the plot beforehand spoils a work of fiction... read no further.
The action takes place over four days, and the young protagonist experiences during those days a lifetime of experiences and emotions. The band of guerrillas in the Spanish mountains during the civil war become Robert Jordan's family and lifelong friends. He first experiences romantic love with the even younger Maria and reflects as he faces his likely death that he considers his life as complete because of the intensity of the four days.
Like the rest of us Robert Jordan has his work, and he sometimes has to put his love for Maria aside to focus on that work which in his case is blowing up a bridge of strategic importance to the cause that he is fighting for. There is his painful resignation that, "the world is a fine place and worth fighting for and I hate very much to leave it." As an outdoorsman, Hemingway always provides the reader with the sights, sounds, and smells of that surrounding world and makes us feel the sadness of anyone having to leave it.