There's a thread about the supernatural which runs throughout For Whom the Bell Tolls. Near the book's beginning, another character, Pilar, appears to see the protagonist's "fate" in his palm. The protagonist, Robert Jordan, makes nothing of it, since he believes superstition is so much stuff and nonsense which doesn't "take the world straight." Throughout the rest of the book, there's something of a competition between Jordan and Pilar, who claims to see into parts of reality to which he is simply "deaf." Many of the other characters are inclined to believe in the supernatural, whether filtered through Pilar or through Spanish Catholicism.
Robert Jordan is completely convinced that belief in the supernatural is "superstition," and is only curious about it because it seems so strange to him.