4 Thus Jonathan spoke well of David to Saul his father, and said to him, "Let not the king sin against his servant, against David, because he has not sinned against you, and because his works have been very good toward you. 5 For he took his life in his hands and killed the Philistine, and the Lord brought about a great deliverance for all Israel. You saw it and rejoiced. Why then will you sin against innocent blood, to kill David without a cause?" 6 So Saul heeded the voice of Jonathan, and Saul swore, "As the Lord lives, he shall not be killed."
Matthew Henry's Commentary on 1 Samuel 19:4-6
Commentary on 1 Samuel 19:1-10
(Read 1 Samuel 19:1-10)
How forcible are right words! Saul was, for a time, convinced of the unreasonableness of his enmity to David; but he continued his malice against David. So incurable is the hatred of the seed of the serpent against that of the woman; so deceitful and desperately wicked is the heart of man without the grace of God, Jeremiah 17:9.