The Sumerians believed that the world was created out of an an ancient sea from whence the universe, gods, and people were created.They believed that the universe was ruled by these gods, who were anthropomorphic (they had human features and personalities) and who represented various natural phenomenon.umerians also believed that the reason for their existence was to delight the gods. The observance of certain rituals and animal sacrifices were considered necessary in order to satisfy these often capricious deities.