17 Saul said to David, "Here is my older daughter Merab. I will give her to you in marriage; only serve me bravely and fight the battles of the Lord." For Saul said to himself, "I will not raise a hand against him. Let the Philistines do that!" 18 But David said to Saul, "Who am I, and what is my family or my clan in Israel, that I should become the king's son-in-law?" 19 So[1] when the time came for Merab, Saul's daughter, to be given to David, she was given in marriage to Adriel of Meholah. 20 Now Saul's daughter Michal was in love with David, and when they told Saul about it, he was pleased. 21 "I will give her to him," he thought, "so that she may be a snare to him and so that the hand of the Philistines may be against him." So Saul said to David, "Now you have a second opportunity to become my son-in-law."

Matthew Henry's Commentary on 1 Samuel 18:17-21

Commentary on 1 Samuel 18:12-30

(Read 1 Samuel 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, Hebrews 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!