Charles H. Spurgeon on Psalms 141:5

Let the righteous smite me; it shall be a kindness, etc. Grace will teach a Christian to take those potions which are wholesome, though they be not toothsome. Faithful reproof is a token of love, and therefore may well be esteemed a kindness. Such wounding of a friend is healing, and so David might well call it an excellent oil. And he did not only say so, which is easy and ordinary, but acted accordingly. He did not as the papists, who highly commend holy water, but turn away their faces when it comes to be sprinkled on them. When he had by sin, and continuance in it, so gangrened his flesh, and corrupted himself, that he was in danger of death, he suffered his sores to be thoroughly searched without regret. Nathan was the chirurgeon whom God employed to search that wound which had divers mouths for festering in his soul; and truly he did not dally with his patient, though he were a prince, but thrust his instrument to the bottom; yet whatever pain it put him to, he took it patiently, and was so far from being angry with the prophet, that he made him one of his privy council. It is a sign of a polluted nature for a man, like a serpent, if he be but touched, to gather poison, and vomit it up at the party. "Rebuke a wise man, and he will love thee": Pr 9:8. —George Swinnock.