From one direction, slander should not land a blow: it is not true. But slander merely means our enemies do not know us well enough to disclose our real sins.
James Denney explains one pang of slander, it hits us on our bruise:
“And David said … let him curse, for the Lord hath bidden him.” 2 Samuel 16:11.
It would be hard to imagine a provocation more exasperating than that which David met in this chastened spirit. As the old King of Israel, once the darling of his people, was making his escape from Jerusalem, a man who had some family connexion with Saul came out to gloat over his downfall. “Come out, come out,” he cried, “thou man of blood, thou man of Belial; the Lord hath returned upon thee all the blood of the house of Saul in whose stead thou hast reigned.” Nothing could have been more malignant and unjust. If David had exterminated the house of Saul when he came to the throne, he would only have done what was common in those times upon a change of dynasty; but in point of fact he had shown for his friend Jonathan’s sake a rare and distinguished generosity to the descendants of his predecessor. He was slandered in the very point on which he might well have prided himself, and we cannot wonder that the combined insolence and falsehood of Shimei provoked the soldiers in his escort. Abishai would have made short work of the malignant Benjamite if only David had allowed him. But David had other thoughts in his heart, and it was the words of Shimei that had roused them. He was not a man of blood, in general terms, but there was blood on his conscience for all that. He was not a man of Belial, in general terms, a worthless vicious character, but there was a hideous tragedy in which he was the villain. It was not the tragedy of the house of Saul, but of the house of Uriah the Hittite. The words of Shimei brought vividly to his remembrance things which touched him more deeply than any human malice could conceive—so deeply that in presence of them resentment could not live. David knew worse about himself than Shimei’s bitter tongue could ever tell. And it is the same with us. The most malignant taunts of our enemies wound us, not by what they are, but by what they remind us of. And in bringing our real sins to remembrance, they not only silence resentment on our part, but call us to reflection, to patience, to humility, to penitence”
James Denney, The Way Everlasting, “Learning From The Enemy”