In Paulo Coelho’s The Alchemist, the characters that are included are a part of the grand scheme of life that the author is trying to convey to the reader. In some ways, the characters are very much like parts of a spider web. Santiago (at the center of the web) feels the effect of what each person does to him or says to him. By meeting each of them—even the young man that robs him—his life is altered, and he is moved along in the direction in which he must go.
The characters often offer help, or wisdom, or lives that are metaphors, serving as examples to Santiago. When Santiago works for the crystal merchant, he sees a man who has missed his chance to pursue his Personal Legend—an experience which provides the impetus for Santiago to eventually continue searching for his Personal Legend.
The Englishman gives Santiago the opportunity to learn from books rather than from the world around him. Book learning is worthless to Santiago, and to the Englisman; where Santiago can see this, the Englishman cannot, and so he makes no progress in searching for his Personal Legend.
Fatima represents true treasure, and therefore, happiness. When Santiago meets her, he realizes that love is one of the greatest treasures in the world, and Fatima is his treasure. He believes at that moment he could die and see to Fatima's happiness, as well as knowing he is one with the world.
The characters in the story either provide, by contrast, information about the character of Santiago, or they are placed in a specific part of the story to move the plot along, while developing the story's themes.
For example, for the theme of "perception," several characters are instrumental in conveying this message to the reader. The old man (Melchizedek) allows Santiago to see the world from a new perspective, as does the alchemist and even the Englishman. The theme of patience is seen when Santiago is forced to work for the crystal merchant in order to replace the money that was stolen from him. Santiago must bide his time, though while he is tempted to turn his back on his Personal Legend.
The characters are formed and "wielded" in a truly effective way by this master "storyteller." Each one is of particular importance, and that is one of the aspects of the novel that is so appealing: there is nothing wasted here, and all the parts provide the perfect balance of "the whole." Paulo Coelho's characters are the "life blood" of his novel's central theme, which is about reaching for one's dreams and never stopping until it is done, regardless of life's obstacles.