Thou knowest Abner the son of Ner,.... Thou canst not be ignorant what a cunning deceitful man he is, nor of his designs; or dost thou not know? art thou ignorant? so read the Septuagint, Vulgate Latin, Syriac, and Arabic versions, with an interrogation:

that he came to deceive thee: with false hopes, or to lead into wrong measures with an intention to involve and ruin him:

and to know thy going out, and coming in; the affairs of his court, the secrets of his government, to observe his conduct and behaviour, and all his actions, and improve them against him:

and to know all that thou doest; he suggests that he came not as a friend, but as a spy, and therefore ought to have been taken up, and detained, and not dismissed. This Joab said to set David against him, fearing, if he should be received into favour, he would be a rival of his; and besides his breast was full of revenge against him for the death of his brother.

Thou knowest Abner the son of Ner, that he came to deceive thee, and to know thy going out and thy coming in, and to know all that thou doest.

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.