2 Then Saul took three thousand chosen men from all Israel, and went to seek David and his men on the Rocks of the Wild Goats. 3 So he came to the sheepfolds by the road, where there was a cave; and Saul went in to attend to his needs. (David and his men were staying in the recesses of the cave.) 4 Then the men of David said to him, "This is the day of which the Lord said to you, 'Behold, I will deliver your enemy into your hand, that you may do to him as it seems good to you.' " And David arose and secretly cut off a corner of Saul's robe. 5 Now it happened afterward that David's heart troubled him because he had cut Saul's robe. 6 And he said to his men, "The Lord forbid that I should do this thing to my master, the Lord's anointed, to stretch out my hand against him, seeing he is the anointed of the Lord."
Matthew Henry's Commentary on 1 Samuel 24:2-6
Commentary on 1 Samuel 24:1-7
(Read 1 Samuel 24:1-7)
God delivered Saul into David's hand. It was an opportunity given to David to exercise faith and patience. He had a promise of the kingdom, but no command to slay the king. He reasons strongly, both with himself and with his men, against doing Saul any hurt. Sin is a thing which it becomes us to startle at, and to resist temptations thereto. He not only would not do this bad thing himself, but he would not suffer those about him to do it. Thus he rendered good for evil, to him from whom he received evil for good; and was herein an example to all who are called Christians, not to be overcome of evil, but to overcome evil with good.