What does 1 Samuel 24:10 mean?

Today you saw with your own eyes how the Lord handed you over to me in the cave. Some wanted me to kill you, but I spared you. I said, 'I won't hurt my master, because he's the Lord's chosen king.' 1 Samuel 24:10 - Modern Text Bible

(David explains that he had the chance to kill Saul but chose not to, out of respect for Saul's role as king.)