Michal, Saul's daughter, loved David: and they told Saul, and the thing pleased him.
"Therefore Saul said to David a second time"  (1 Samuel 18:21).  This is either a summary of what Saul was about to do through his servants as intermediaries, which is possible, or a direct proposition to David.  If it was the latter, David did not bother to reply; he had already been frustrated by Saul's false promises.  At any rate, Saul employed his servants in an effort to persuade David to marry his daughter.  David's explanation that he was not able to give the king a marriage present may also explain what prevented his marriage to Merab.  If so, Saul's scheme to get David killed could have been tied to that very thing; and Saul promptly took advantage of it.