Why does Kino come to feel that he will lose his soul if he gives up the pearl?

KIno thinks the pearl is they key to bettering his family and giving him a sense of manhood he never had. Kino wants to send his child to school. He wants his wife to have nice clothes and he never wants to beg for a doctor (like an animal) like he did before. These illusions control Kino and cloud his judgment.