Wherefore when Saul saw that he behaved himself very wisely, he was afraid of him.

Matthew Henry's Concise Commentary

18:12-30 For a long time David was kept in continual apprehension of falling by the hand of Saul, yet he persevered in meek and respectful behaviour towards his persecutor. How uncommon is such prudence and discretion, especially under insults and provocations! Let us inquire if we imitate this part of the exemplary character before us. Are we behaving wisely in all our ways? Is there no sinful omission, no rashness of spirit, nothing wrong in our conduct? Opposition and perverseness in others, will not excuse wrong tempers in us, but should increase our care, and attention to the duties of our station. Consider Him that endured contradiction of sinners against himself, lest ye be weary and faint in your minds, Heb 12:3. If David magnified the honour of being son-in-law to king Saul, how should we magnify the honour of being sons to the King of kings!