Hemingway is one of those writers whose work is just ageing out of relevancy. He relies a lot on context that people no longer have.

World War 1 was such a world changing conflict that it's hard to imagine now. Not just the violence itself but the way it changed how people looked at the world.

This book is very much Hemingway trying to make sense of his own experiences of the Italian front and he'd be the first to admit that he struggled turning it into a coherent story. He wrote dozens of endings for the book and wasn't happy with any of them.