Moab — For although the king of Moab, out of hatred to Saul, gave protection to his parents, 1 Samuel 22:3-4, yet the Moabites were perpetual and sworn enemies to the Israelites, who therefore were forbidden to admit them into the congregation of the Lord. And though God commanded them in their march to Canaan, to spare the Moabites, yet afterwards they proved fierce enemies to God and his people, and thereby provoked God to alter his carriage towards them. Measured them — That is, having conquered the land, he made an estimate of it, and distributed the towns and people into three parts. Casting down — Overthrowing their towns, and utterly destroying their people in manner following. And now that prophecy, Numbers 24:17, was accomplished.
Related Commentaries of 2 Samuel 8:2
2 Samuel 8:2
2 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.