Do therefore according to thy wisdom, and let not his hoary head go down to hell in peace.

“[David] orders Solomon to punish [Joab], not out of viciousness or hatred for him but because he knew that he was wicked and that, if he had acted with hostility against him who was a mature man, he would act even worse against a young man, so that the kingdom would become unstable, and the house would not be firmly established. Therefore he entrusts his son with the revenge against him who had offended him, in order that, after the killing of that evil man by the hand of the new king, he might be feared by everyone, and no revolt might ever occur.”

“Do therefore according to thy wisdom,.... Which though young began to appear in him, even in the life of his father; he therefore exhorts him to use the wisdom he had, and take the first and fittest opportunity to cut him off for his former murders and late treason, as a dangerous man to his government and the peace of it: and let not his hoary head go down to the grave in peace; that is, let him not die a natural, but a violent death; and let not his grey hairs be any argument for sparing him, or any reason for delaying the taking of him off, because he would in course die quickly; for he must be now an old man, as old as David, or perhaps older; since he had been his general forty years, even all the time of his reign; see Sa2 2:13.”

“Let not his hoar head go down to the grave in peace - It would have been an insult to justice not to have taken the life of Joab. David was culpable in delaying it so long; but probably the circumstances of his government would not admit of his doing it sooner. According to the law of God, Joab, having murdered Abner and Amasa, should die. And had not David commanded Solomon to perform this act of justice, he could not have died in the approbation of his Maker.”

“Servants, or subjects. The king of Israel has thus a plea to interest all his people, as the danger was common. (Salien) — He assumes the character of disinterestedness, as if he had been willing to abandon all his private property; knowing that Benadad would not accede even to that hard proposal. (Haydock) — Thus “Nero consulted the first men of the city, whether they would prefer a doubtful war or a disgraceful peace.” (Tacitus, An. xv.)”