He called David, the shepherd, to his palace because David was good at playing the harp, and the soft music soothed Saul when he was being tormented by the evil spirit. Saul "liked him very much, and David became one of his armor-bearers." So, "...whenever the spirit from God came upon Saul, David would take his harp and play. Then relief would come to Saul; he would feel better, and the evil spirit would leave him." He unknowingly puts in his court the person God chose to replace him.