When the American and Mexican cowboys ride up into the hills to capture wild horses, an elderly Mexican man serves as their mozo, or camp hand and cook. John Grady is disturbed by the wild horses’s behavior after they are penned up. The way they squeal and kick and bite makes him wonder about the essential nature of horses. The confined wild animals seem “as if they were no more than some evil dream of a horse.” At camp that night, Luis tells them about his long-ago wartime experiences when he, along with his father and brothers, served in the cavalry. He had learned the most about horses by being with them when they died. Luis says,

the souls of horses mirror the souls of men more closely than men suppose…

Elaborating on the analogy between war and their current situation, Luis speculates further about horses’s souls. He believes that all horses share a common soul, out of which each individual horse draws its separate, mortal self. It is in answer to John Grady’s question about men’s souls that Luis speaks the quoted line. The “communion. . .among horses” refers to this common soul from which they originate, which is a distinct situation than the way that men arise. Because men lack this spiritual commonality, it may not be possible to understand them. Luis implies that humans must expend the effort to understand the horses, not the other way around.