1 Kings 2:9

hold him not guiltless i.e. Be sure not to let him go unpunished. Find out some good reason for vengeance to be taken on him. We are not to wonder at these injunctions of David, which were not unnatural, both for the satisfaction of his own feelings and for providing for the security of Solomon's throne. Joab was a dangerous man to be left alive, and Shimei, with Oriental fickleness, would curse Solomon as readily as he had cursed David, should a reverse of fortune come upon him. Nor are we to look for New Testament virtues in even the best men of the older covenant. The Christian thinks it nobler to forgive, following the lessons of his master, but what David saw of Christ was in the less clear vision of faith, and neither he nor his people are to be expected to rise in any great degree towards the nobility of Christian forgiveness. Yet David was very generous toward Saul. He seems to have become less forgiving in his old age, though doubtless he was thinking chiefly of Solomon's safety.