What is coelhos purpose for asking Santiago to become the counselor of the oasis?

Santiago tells the chiefs and, after some deliberation, they decide to ready themselves for war - even though this is against the tradition of the oasis, which is usually considered neutral ground. The chiefs make a stipulation: if the enemy arrives, the chief will give Santiago a piece of gold for every 10 enemies slain; if Santiago's vision is wrong, he will be killed.  The next day, 500 armed tribesmen enter the oasis as Santiago has predicted. The men of the oasis, duly warned, kill all of the intruders and the chieftain of the oasis awards Santiago 50 pieces of gold and asks him to become the oasis's counselor.