David needed to know he would be king years before he actually became king. The intervening years gave David the time he needed to study and train for military and political leadership. Once David became Saul’s armor bearer, David was in the ideal position to do that. At first, Saul did not know that David was to be king after him. If he had known, he would have tried to kill David immediately. As it was, Saul grew to hate David anyway. Actually, Saul grew to hate a lot of people.