What reasons does Melchizedek give for demanding payment of one tenth of the flock for advice about finding the treasure from the alchemist?

Melchizedek explains that demanding one-tenth of the flock serves as a test of Santiago's commitment and faith in his journey. By giving a portion of his earnings, Santiago demonstrates his willingness to invest in his own dreams and the pursuit of his Personal Legend. Additionally, Melchizedek emphasizes that this act symbolizes the universal principle of reciprocity, where giving leads to receiving greater wisdom and abundance. Ultimately, it reinforces the idea that the universe conspires to help those who are dedicated to their aspirations.