Writers use symbolism to explain an idea or concept to their readers in a poetic manner without saying it outright.
Hemingway was a master of this technique, so this book is full of symbolism, beginning with the title, but much of it boils down to a writer obsessed with masculinity. That obsession takes us to bullfighting, which is symbolic of sexual seduction when two beings face each other in a game of skill, where one wins and the,e other is hurt or even killed with a sword. Sex seems to symbolize masculinity rather than an object of i.
The story starts in Paris, which symbolizes romance, where Jake's lost love, Brett, meets with him. He tells her of a war wound that has left him impotent. Brett tells him she loves and always will, but she rejects him because of his impotence. Jake gathers some friends from the lost generation, and they go to Spain for the bullfights and other macho activities. Brett goes with them.
The chapters on bullfighting flip back and forth, complimenting their fly fishing trip, drinking, sex other very masculine activities.
Hemingway's outlook seems to be summed up by two of his characters, Cohn and Jake, when they say, "I can't stand it to think my life is going so fast and I'm not living it." "Nobody ever lives life all the way up except bullfighters."