And he smote Moab, and measured them with a line, casting them down to the ground; even with two lines measured he to put to death, and with one full line to keep alive. And so the Moabites became David’s servants, and brought gifts.
God had given David rest from all his enemies that opposed him and made head against him; and he having made a good use of that rest, has now commission given him to make war upon them, and to act offensively for the avenging of Israel's quarrels and the recovery of their rights; for as yet they were not in full possession of that country...
Commenting on 2 Samuel 8:1-8
And he smote Moab,.... He next went against that, and invaded it, the people of it being always troublesome and distressing to the children of Israel; and though the king of it had shown some favour to David, yet it was when he considered him as an enemy to Saul, and Saul to him; but things having taken a different turn, his and his people's...
he smote Moab, and measured them with a line--This refers to a well-known practice of Eastern kings, to command their prisoners of war, particularly those who, notorious for the atrocity of their crimes or distinguished by the indomitable spirit of their resistance, had greatly incensed the victors, to lie down on the ground.