I Samuel 24:20

This wish was expressed in perfect sincerity. David's behaviour towards him had conquered for the moment the evil demon of his heart, and completely altered his feelings. In this better state of mind he felt impelled even to give utterance to these words, "I know that thou wilt be king, and the sovereignty will have perpetuity in thy hand." Saul could not prevent this conviction from forcing itself upon him, after his own rejection and the failure of all that he attempted against David; and it was this which drove him to persecute David whenever the evil spirit had the upper hand in his soul. But now that better feelings had arisen in his mind, he uttered it without envy, and merely asked David to promise on oath that he would not cut off his descendants after his death, and seek to exterminate his name from his father's house. A name is exterminated when the whole of the descendants are destroyed, - a thing of frequent occurrence in the East in connection with a change of dynasties, and one which occurred again and again even in the kingdom of the ten tribes (vid., Kg1 15:28., Sa1 16:11.; 2 Kings 10).

We have hitherto had Saul seeking an opportunity to destroy David, and, to his shame, he could never find it. In this chapter David had a fair opportunity to destroy Saul, and, to his honour, he did not make use of it; and his sparing Saul's life was as great an instance of God's grace in him as the preserving of his own life was of God's providence over him. Observe, I. How maliciously Saul sought David's life (Sa1 24:1, Sa1 24:2). II. How generously David saved Saul's life (when he had him at an advantage) and only cut off the skirt of his robe (Sa1 24:3-8). III. How pathetically he reasoned with Saul, upon this to bring him to a better temper towards him (Sa1 24:9-15). IV. The good impression this made upon Saul for the present (Sa1 24:16-22).

24:20 I realize that you are surely going to be king: This was Saul’s first open admission of the truth (cp. 23:17).