Anger led Saul to try to kill his son Jonathan.

He was pissed off at David, because David was honoring God and growing in popularity.

Saul tried to kill him time and time again but could not, which made him afraid of him.

Jonathan, Saul's son, was best friends with David and helped protect him. For this, Saul almost killed his own son.

The moral of the story, is that your anger, if unleashed can inflict mortal harm to those you love the most.