A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
1 Kings (1 Samuel) 24:2
sa1 24:2DAVID IN A CAVE AT ENGEDI CUTS OFF SAUL'S SKIRT, BUT SPARES HIS LIFE. (Sa1 24:1-7)
Saul . . . went . . . to seek David . . . upon the rocks of the wild goats--Nothing but the blind infatuation of fiendish rage could have led the king to pursue his outlawed son-in-law among those craggy and perpendicular precipices, where were inaccessible hiding places. The large force he took with him seemed to give him every prospect of success. But the overruling providence of God frustrated all his vigilance.
1 Kings (1 Samuel) 24:3
sa1 24:3he came to the sheepcotes--most probably in the upper ridge of Wady Chareitun. There a large cave--I am quite disposed to say the cave--lies hardly five minutes to the east of the village ruin, on the south side of the wady. It is high upon the side of the calcareous rock, and it has undergone no change since David's time. The same narrow natural vaulting at the entrance; the same huge natural chamber in the rock, probably the place where Saul lay down to rest in the heat of the day; the same side vaults, too, where David and his men were concealed. There, accustomed to the obscurity of the cavern, they saw Saul enter, while, blinded by the glare of the light outside, he saw nothing of him whom he so bitterly persecuted.
1 Kings (1 Samuel) 24:4
sa1 24:4the men of David said . . . Behold the day of which the Lord said unto thee, Behold, I will deliver thine enemy into thine hand--God had never made any promise of delivering Saul into David's hand; but, from the general and repeated promises of the kingdom to him, they concluded that the king's death was to be effected by taking advantage of some such opportunity as the present. David steadily opposed the urgent instigations of his followers to put an end to his and their troubles by the death of their persecutor (a revengeful heart would have followed their advice, but David rather wished to overcome evil with good, and heap coals of fire upon his head); he, however, cut off a fragment from the skirt of the royal robe. It is easy to imagine how this dialogue could be carried on and David's approach to the king's person could have been effected without arousing suspicion. The bustle and noise of Saul's military men and their beasts, the number of cells or divisions in these immense caverns (and some of them far interior) being enveloped in darkness, while every movement could be seen at the cave's mouth--the probability that the garment David cut from might have been a loose or upper cloak lying on the ground, and that Saul might have been asleep--these facts and presumptions will be sufficient to account for the incidents detailed.
1 Kings (1 Samuel) 24:8
sa1 24:8HE URGES THEREBY HIS INNOCENCY. (Sa1 24:8-15)
David also arose . . . and went out of the cave, and cried after Saul--The closeness of the precipitous cliffs, though divided by deep wadies, and the transparent purity of the air enable a person standing on one rock to hear distinctly the words uttered by a speaker standing on another (Jdg 9:7). The expostulation of David, followed by the visible tokens he furnished of his cherishing no evil design against either the person or the government of the king, even when he had the monarch in his power, smote the heart of Saul in a moment and disarmed him of his fell purpose of revenge. He owned the justice of what David said, acknowledged his own guilt, and begged kindness to his house. He seems to have been naturally susceptible of strong, and, as in this instance, of good and grateful impressions. The improvement of his temper, indeed, was but transient--his language that of a man overwhelmed by the force of impetuous emotions and constrained to admire the conduct, and esteem the character, of one whom he hated and dreaded. But God overruled it for ensuring the present escape of David. Consider his language and behavior. This language--"a dead dog," "a flea," terms by which, like Eastern people, he strongly expressed a sense of his lowliness and the entire committal of his cause to Him who alone is the judge of human actions, and to whom vengeance belongs, his steady repulse of the vindictive counsels of his followers; the relentings of heart which he felt even for the apparent indignity he had done to the person of the Lord's anointed; and the respectful homage he paid the jealous tyrant who had set a price on his head--evince the magnanimity of a great and good man, and strikingly illustrate the spirit and energy of his prayer "when he was in the cave" (Psa 142:1).