You might like to approach this question through considering the way in which omens are used in this novel. The occurrence of omens is particularly noticable in Santiago's spiritual quest, and they seem to have two main functions in the story. Firstly, they seem to confirm Santiago and offer him guidance as he embarks on his journey. Melchizedek seems to support this interpretation when he explains to Santiago how omens are part of what he refers to as the Universal Language of the World. He tells Santiago that if he learns to tune into this language he will always be able to find the significance of his setting. Omens thus strengthen the theme of the unity that is within nature.
However, the way that omens are used and refered to in the text are also part of the character development of Santiago, as they grow from being very limited to omens that become significant visions that impact many people. Consider the vision that Santiago experiences in Al-Fayoum where he sees the hawks and armies that warns him of a potential assault that would result in the slaughter of a large number of people. The way that such omens clearly become more and more important act as a kind of marker of the way that Santiago is understanding more of the Language of the World that clearly indicates his increasing maturity.