1 And after this it came to pass, that David smote the Philistines, and subdued them: and David took Metheg-ammah out of the hand of the Philistines. 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. 3 David smote also Hadadezer, the son of Rehob, king of Zobah, as he went to recover his border at the river Euphrates. 4 And David took from him a thousand chariots, and seven hundred horsemen, and twenty thousand footmen: and David houghed all the chariot horses, but reserved of them for an hundred chariots. 5 And when the Syrians of Damascus came to succour Hadadezer king of Zobah, David slew of the Syrians two and twenty thousand men. 6 Then David put garrisons in Syria of Damascus: and the Syrians became servants to David, and brought gifts. And the LORD preserved David whithersoever he went. 7 And David took the shields of gold that were on the servants of Hadadezer, and brought them to Jerusalem. 8 And from Betah, and from Berothai, cities of Hadadezer, king David took exceeding much brass. 9 When Toi king of Hamath heard that David had smitten all the host of Hadadezer, 10 Then Toi sent Joram his son unto king David, to salute him, and to bless him, because he had fought against Hadadezer, and smitten him: for Hadadezer had wars with Toi. And Joram brought with him vessels of silver, and vessels of gold, and vessels of brass: 11 Which also king David did dedicate unto the LORD, with the silver and gold that he had dedicated of all nations which he subdued; 12 Of Syria, and of Moab, and of the children of Ammon, and of the Philistines, and of Amalek, and of the spoil of Hadadezer, son of Rehob, king of Zobah. 13 And David gat him a name when he returned from smiting of the Syrians in the valley of salt, being eighteen thousand men. 14 And he put garrisons in Edom; throughout all Edom put he garrisons, and all they of Edom became David's servants. And the LORD preserved David whithersoever he went. 15 And David reigned over all Israel; and David executed judgment and justice unto all his people. 16 And Joab the son of Zeruiah was over the host; and Jehoshaphat the son of Ahilud was recorder; 17 And Zadok the son of Ahitub, and Ahimelech the son of Abiathar, were the priests; and Seraiah was the scribe; 18 And Benaiah the son of Jehoiada was over both the Cherethites and the Pelethites; and David's sons were chief rulers.
[AD 420] Jerome on 2 Samuel 8:1-5
In the second book of Kings [Samuel], where David defeated the Moabites, Scripture records the measuring out of two separate lines for life and two for death. The significance of setting aside some Moabites for life and others for death is made clear by the story of Orpah and Ruth. Orpah, who turned back to idolatry and her ancient country, was destined for death; Ruth, following her mother-in-law, whose name means “pleasant,” says, “Your people shall be my people, and your God my God.”

[AD 585] Cassiodorus on 2 Samuel 8:1-5
The history of the Kings [Samuel] recounts that David won these victories after he succeeded Saul in the kingship, and it seems inappropriate to introduce them into our ordered arrangement here since they are known to be recounted extensively there. But we must realize that these wars are a description in figure of the Lord Savior’s victories which he wins throughout the whole world over pagans and the faithless. It is their words which this psalm will utter, so that when truly dislodged from their old superstition they may deserve to be changed through the grace of the new man.

[AD 735] Bede on 2 Samuel 8:2
"And he struck down Moab, and measured them with a line, aligning them to the ground, etc." [2 Samuel 8:2] What is written about David: "And he smote Moab, and measured them with a line, laying them on the ground," should be understood hyperbolically. For it was not possible that men living on the earth would be so humbled that, lying on the ground, they would appear equal with the ground itself, as confirmed by a line stretched over them; but the Scripture wanted to accumulate the immense humiliation of the captured and oppressed nation with this word, to say they were made equal to the ground, as if by God they were emasculated and despised, so that they living on earth no longer mattered more than the ground that had no people. You have many examples of this kind of expression in the Scriptures, such as that one from the Gospel: "And there are also many other things which Jesus did; if they were written every one, I suppose that even the world itself could not contain the books that should be written" (John XXI). For how could the world not contain the books that could have been written in the world? But to imply the greatness and multitude of the Lord's deeds, the Scripture wished to use such an expression. And in David's lament, "They were swifter than eagles, stronger than lions" (II Samuel I). Which is similar to that secular expression: "Who would surpass the whiteness of snow, in their courses the winds." That he said "measured them with a line," he put the line allegorically for destiny, because fields are usually measured by a line. Hence it is written: "And he divided the land to them by lot with a measuring line." It means that David would distribute the regions of the Moabites to the heirs according to his will, as freely as any possessor might divide his own fields at his whim by stretching the line here and there. He measured two lines, one for putting to death, and one for keeping alive. And this is said allegorically, signifying that David had the power, with no one contradicting, to put to death those who were rebellious and to spare those who were submissive.

[AD 1781] Richard Challoner on 2 Samuel 8:16
Recorder: Or chancellor.
[AD 1781] Richard Challoner on 2 Samuel 8:17
Scribe: Or secretary.
[AD 1781] Richard Challoner on 2 Samuel 8:18
The Cerethi and Phelethi: The king's guards.-- Ibid.
[AD 1781] Richard Challoner on 2 Samuel 8:18
Princes: Literally priests. (Cohen) So called, by a title of honour, and not from exercising the priestly functions.