1 Samuel 18:21
And Saul said, I will give him her, that she may be a snare to him, and that the hand of the Philistines may be against him. Wherefore Saul said to David, Thou shalt this day be my son in law in the one of the twain. And Saul said, I will give him her, that she may be a snare to him, and that the hand of the Philistines may be against him. Wherefore Saul said to David, Thou shalt this day be my son in law in the one of the twain.
Saul offered David marriage to one of his two daughters, declaring that David would on that very day become his son-in-law. The offer was not made in good faith but concealed settled hostility beneath a show of favor. It was designed as a snare, using the marriage bond to draw David into a position of exposure and peril. By that means Saul intended to bring the hand of the Philistines against David, so that his enemies would do the work of destroying him.