How is the king important in the story?

Melchizedek is the king of Salem, a mysterious far-off land. Melchizedek appears to Santiago in the town square of Tarifa, where he tells Santiago about the Soul of the World and his Personal Legend for the first time. Melchizedek always appears to people who are trying to live their Personal Legend, even if they don't know it. While he appears at first to be dressed in common Arab dress, at one point he pulls aside his cloak to reveal a gold breastplate encrusted with precious stones. He also gives Santiago the magical stones Urim and Thummim.