He smote Moab— It is frequent in the sacred writings to put the inhabitants of a country for the country itself: see Isaiah 15:4. The LXX favour this interpretation, and thus Grotius understands it. And to this the Psalmist seems plainly to refer, when, speaking of the wars of David with Moab, Edom, and other nations, he says, I will divide Sechem, and mete out the valley of Succoth, viz. in order to divide it. Psalms 60:6. He measured them with a line. The measurement of lands was formerly by the line, as now it is generally done by the rod; and because lands were divided into certain tracts and portions by the line, hence the line is often put for the tract marked out by it, or even where the line had never been made use of at all. Thus, all the region of Argob, Deuteronomy 3:4 is in the original חבל כל kal chebel, all the line of Argob. So the line of the sea, Zephaniah 2:5-7 is the sea-coast. Thus in the place before us, he measured them by line, i.e. divided the country of the Moabites into several parts, that he might the better know what towns it was most proper to demolish, to level with the ground, and to extirpate the inhabitants of them. Even with two lines, &c. The ancient versions read differently from our present text. The Vulgate, he measured two lines, one to kill, and one to keep alive. The Septuagint differently, but to the same sense, there were two lines for putting to death, and two for taking alive; according to which accounts, one half of the inhabitants only were put to death. And it appears from the text itself, that it should be thus understood. The words in the original are, חבלים שׁני וימדד vaimadded shenei chabalim, And he measured two lines. Repeat from the foregoing words, חבל chebel, a line, להמית lehamith, to put to death, להחיות החבל ומלא umlo hachebel lehachayoth; and the fulness of a line to keep alive. This supplement is natural and agreeable to the language. Many instances may be produced. Thus, Psalms 110:3 what we render, almost without any sense, from the womb of the morning thou hast the dew of thy youth, becomes an elegant expression if we repeat the word dew. The dew of thy youth is as the dew from the womb of the morning. The verse here then should be rendered, "And he measured two lines; i.e. divided the country into two parts; a line, i.e. a tract for death; and the plenitude of the line, i.e. a very large tract of the country for life, to destroy the inhabitants of the one, and preserve the inhabitants of the larger part." The first clause of the verse, he measured them with a line, &c. signifies no more than that David smote Moab, i.e. the country and its inhabitants, and measured them with a line; i.e. took an exact survey of the towns, and cities, and strongholds of the whole land, ארצה אותם השׁכב hashkeb otham artzah, to throw them down to the ground; i.e. to destroy and level them to the ground, as far as he thought necessary to humble them, and to secure himself. The expression, fulness of a line, seems to denote a very large tract of country, and might be a larger than that where the inhabitants were ordered to be put to death.
The Moabites became David's servants— Who was the aggressor in these two last actions, is not said; but it may be collected from Psalms 83 that Edom, Moab, Ammon, Amalek, and others, consulted together to cut off Israel from being a nation, which seems to refer to the wars mentioned in this chapter. However, it may be remarked, that the Philistines, Moabites, and other neighbouring nations, were perpetual enemies of the Jews, and invaded them whenever they were able; and that therefore the Jews thought they had a right to make reprisals, and to attack them upon every occasion. See Numbers 24:17; Numbers 24:25 where this event is foretold.