22 Just then the servants of David arrived with Joab from a raid, bringing much spoil with them. But Abner was not with David at Hebron, for he had sent him away, and he had gone in peace. 23 When Joab and all the army that was with him came, it was told Joab, "Abner the son of Ner came to the king, and he has let him go, and he has gone in peace." 24 Then Joab went to the king and said, "What have you done? Behold, Abner came to you. Why is it that you have sent him away, so that he is gone? 25 You know that Abner the son of Ner came to deceive you and to know your going out and your coming in, and to know all that you are doing." 26 When Joab came out from David's presence, he sent messengers after Abner, and they brought him back from the cistern of Sirah. But David did not know about it. 27 And when Abner returned to Hebron, Joab took him aside into the midst of the gate to speak with him privately, and there he struck him in the stomach, so that he died, for the blood of Asahel his brother. 28 Afterward, when David heard of it, he said, "I and my kingdom are forever guiltless before the Lord for the blood of Abner the son of Ner. 29 May it fall upon the head of Joab and upon all his father's house, and may the house of Joab never be without one who has a discharge or who is leprous or who holds a spindle or who falls by the sword or who lacks bread!" 30 So Joab and Abishai his brother killed Abner, because he had put their brother Asahel to death in the battle at Gibeon.
Matthew Henry's Commentary on 2 Samuel 3:22-30
Commentary on 2 Samuel 3:22-39
(Read 2 Samuel 3:22-39)
Judgments are prepared for such scorners as Abner; but Joab, in what he did, acted wickedly. David laid Abner's murder deeply to heart, and in many ways expressed his detestation of it. The guilt of blood brings a curse upon families: if men do not avenge it, God will. It is a sad thing to die like a fool, as they do that any way shorten their own days, and those who make no provision for another world. Who would be fond of power, when a man may have the name of it, and must be accountable for it, yet is hampered in the use of it? David ought to have done his duty, and then trusted God with the issue. Carnal policy spared Joab. The Son of David may long delay, but never fails to punish impenitent sinners. He who now reigns upon the throne of David, has a kingdom of a nobler kind. Whatever He doeth, is noticed by all his willing people, and is pleasing to them.