Matthew Poole and continuators on 2 Samuel 3:39

39 And I am this day weak , though anointed king; and these men the sons of Zeruiah be too hard for me : the LORD shall reward the doer of evil according to his wickedness.

Or, tender, in the Infancy of my Kingdom, not well rooted and settled in it. The Metaphor is taken from a young and tender Child or Plant.

Ioab and Abishai, the Sons of my Sister Zeruiah.

i. e. Too powerful. They have so great a command over all the Soldiers, and so great favour with the People, that I cannot Punish them without apparent hazard to my Person, and Kingdom; especially, now when all the Tribes, except Iudah, are yet in a state of Opposition against me. But this, although it might give some colour to the delay of their Punishment for a season, yet it may seem to have been one of David's infirmities, that he did not do it within some reasonable time, both because this Indulgence proceeded from a distrust of Gods Power and Faithfulness; as if God could not, or would not make good his Promise of the Kingdom to him, without, and against Ioab and all his Confederates; and because it was contrary to Gods Law, which severely requires the Punishment of Wilful Murderers, Gen. 9. 6. Exod. 21. 14. Numb. 35. 21. which David had no power to dispence with. And David might, and should have remembred, how dear Saul pay'd for this very thing, that he dispensed with Gods Command, and spared those whom God commanded him to slay, 1 Sam. 15. And it seems David's Conscience oft smote him for this: which made him watch for a fit opportunity to remove, and then punish him, and having neglected it till Death, he declareth his sorrow for that neglect, by giving Solomon a charge to execute it after his Death, 1 King. 2. 5, 6, 34.

Marginal references: Heb. tender.; Chap. 19. 7.; See Chap. 20. 10.; 1 King. 2. 5, 6, 33, 34.