when one told me, ‘Behold, Saul is dead,’ and thought he was bringing good news, I seized him and killed him at Ziklag, which was the reward I gave him for his news.
We have here justice done upon the murderers of Ish-bosheth. I. Sentence passed upon them. There needed no evidence, their own tongues witnessed against them; they were so far from denying the fact that they gloried in it. David therefore shows them the heinousness of the crime, and that blood called for blood from his hand, who was now the chief magistrate, and was by office the avenger of blood.
Commenting on 2 Samuel 4:9-12
How much more, when wicked men have slain a righteous person,.... As Ishbosheth was in comparison of the wicked men that slew him; though not with respect to David, if he knew of his divine designation to the throne; nor with respect to Mephibosheth his eldest brother's son, whose right to the throne was prior to his, which he must know; though with respect to...
A reward for his tidings - Ὡ εδει με δουναι ευαγγελια, Septuagint. Here is a proof that ευαγγελιον, evangelium or gospel, signifies the reward which the bringer of good tidings is entitled to receive. See my preface to St. Matthew's Gospel.