When the caravan is crossing the desert, the Englishman lends Santiago his books. Santiago and the Englishman were speaking earlier about each of their individual treasure hunts. The Englishman is very interested in hearing about what Santiago has learned through experience rather than books. Santiago has learned to listen and watch the world around him, and he has started to see that many things around him are speaking the same language.
The Englishman is quite different. He learns about the world through his books and through studying the ancient texts. It's how he plans to learn about alchemy. To the Englishman's credit, he admits that he can perhaps learn more about alchemy and the language of the world by adopting some of Santiago's practices. Santiago in turn admits that he should probably read some of the books that the Englishman values so highly.
The Englishman then loans Santiago his books, but Santiago is frustrated by the complexity of the books. Santiago gives it a good effort, and he asks the Englishman a lot of questions, but Santiago ultimately decides to go back to observing nature and the world around him. The Englishman gives up on Santiago's method and returns to his books.