Why do you think the alchemist tells Santiago the story about the man's dream about the two sons (the poet and the soldier)

The story that the alchemist tells Santiago about Emperor Tiberius and his sons appears to hold the lesson that, although a person may not have a destiny he expects or even desires, if that person acts in accordance with his own desires, he will serve a purpose greater than himself. In the story, which appears in the Bible in Matthew 8:5-8, a centurion demonstrates his faith in Jesus, acknowledging that if Jesus just speaks a word he can heal the centurion’s servant, who is paralyzed and suffering. The angel tells Tiberius that, although the centurion did not intend to be remembered for this speech, his words have become immortal. This story reiterates the notion that in living out his Personal Legend, Santiago served not only himself but also the Soul of the World. Also, just like the Narcissus story from the beginning of The Alchemist, this story takes a well-known narrative, this time a story from the Bible, and adds another dimension to it, giving it a new meaning in the context of the novel.