Matthew Poole and continuators on 1 Samuel 18:25

25 And Saul said, Thus shall ye say to David, The king desireth not any dowry, but an hundred fore-skins of the Philistines, to be avenged of the kings enemies. But Saul thought to make David fall by the hand of the Philistines.

These he desires rather than their heads; partly, for the greater convenience of bringing them, and presenting them before him; partly, to cover his malice against David with a pretence of Zeal for God, and for his People, and for the Covenant of Circumcision; and partly, that the Philistines might be the more enraged against David for this reproachful and Barbarous usage of them, and might therefore watch all opportunities to destroy him.