What does 1 Samuel 18:21 mean?

Saul thought, 'I'll give her to him, and she'll be a trap for him, so the Philistines will kill him.' So Saul said to David, 'You can marry my second daughter today.' 1 Samuel 18:21 - Modern Text Bible

(Saul's plan is to use Michal's love for David as a way to put David in harm's way.)