Charles Ellicott Commentary 1 Samuel 18:19

"But it came to pass at the time when Merab, Saul`s daughter, should have been given to David, that she was given unto Adriel the Meholathite to wife." — 1 Samuel 18:19 (ASV)

She was given to Adriel. —Saul’s capricious wavering nature, so painfully prominent in the last part of his reign, displayed itself in this sudden change of purpose. It may have been brought about because of some great fit of jealousy of David; or possibly the large gifts in money or valuables offered by the wealthy Adriel for the princess’s hand may have caused this arbitrary act of Saul. Such gifts to the father in return for the daughter’s hand were customary. In the case of such a prize as the Princess Merab, the gift would doubtless have been very costly.

David, who was comparatively a poor man, was of course unable to show such liberality; besides, the young hero looked, no doubt, upon the marriage as the fulfilment of the old promise to the victor in the combat with the giant. The marriage, however, of the daughter of King Saul and Adriel was consummated, and was disastrous in its consequences. They had five sons, and they fell victims to the blood revenge exacted by the Gibeonites from the family of Saul: the five hapless youths were hanged (we read in 2 Samuel 21:9) in the hill before the Lord. These three verses (17-19) are entirely omitted by the Septuagint, apparently because they failed to see any reason for Saul’s sudden change of purpose.