Charles Ellicott Commentary 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 a second time." — 1 Samuel 18:21 (ASV)

That she may be a snare to him. —Is it not possible that this dark plot of Saul against a life once so dear to him—a plot which in later days, when the king's enmity was a matter of general notoriety, of course became known to David—suggested to him (David) the means by which, in the darkest hours of his life, he got rid of the brave Uriah, the husband of Bath-sheba, at the siege of Rabbah? (2 Samuel 11:0)

In the one of the two. —More accurately translated: in this second time, or in this second way. The Septuagint again leaves out this statement, no doubt because it refers back to the omitted passage in 1 Samuel 18:17–19.