Commentaries
4:8-12 A person may be glad to obtain his just wishes, and yet really regret the means by which he receives them. He may be sorry for the death of a person by which he is a gainer. These men shed innocent blood, from the basest motives. David justly executed vengeance upon them. He would not be beholden to any to help him by unlawful practices. God had helped him over many a difficulty, and through many a danger, therefore he depended upon him to crown and complete his own work. He speaks of his redemption from all adversity, as a thing done; though he had many storms yet before him, he knew that He who had delivered, would deliver.
8. They brought the head of Ish-bosheth unto David … and said, Behold the head of Ish-bosheth—Such bloody trophies of rebels and conspirators have always been acceptable to princes in the East, and the carriers have been liberally rewarded. Ish-bosheth being a usurper, the two assassins thought they were doing a meritorious service to David by removing the only existing obstacle to the union of the two kingdoms.