Charles H. Spurgeon on Psalms 141:5

The righteous, etc. The minister cannot be always preaching; two or three hours, may be, in a week, he spends among his people in the pulpit, holding the glass of the gospel before their faces; but the lives of professors, these preach all the week long: if they were but holy and exemplary, they would be as a repetition of the preacher's sermon to their families and neighbours among whom they converse, and keep the sound of his doctrine continually ringing in their ears. This would give Christians an amiable advantage in doing good to their carnal neighbours by counsel and reproof, which now is seldom done, and when done it proves to little purpose, because not backed with their own exemplary walking. "It behooves him", saith Tertullian, "that would counsel or reprove another, to guard his speech with the authority of his own conversation, lest, wanting that, what he says puts himself to the blush." We do not love one that hath a stinking breath to come very near us; such, therefore, had need have a sweet scented life. Reproofs are a good physic, but they have an unpleasant reception; it is hard for men not to throw them back on the face of him that gives them. Now nothing is more powerful to keep a reproof from thus coming back than the holiness of the person that reproves. "Let the righteous smite me", saith David, "it shall be a kindness: and let him reprove me; it shall be an excellent oil, which shall not break my head." See how well it is taken from such a hand, from the authority that holiness carries with it. None but a vile wretch will smite a righteous man with reproach for smiting him with a reproof, if softly laid on, and like oil fermented, and wrought into him, as it should, with compassion and love to his soul! Thus we see how influential the power of holiness would be unto the wicked, neither would it be less upon our brethren and fellow Christians. Holy David professed he would take it as a kindness for the righteous man to smite him; yea, as kindly as if he broke a box of precious oil upon his head, which was amongst the Jews a high expression of love. —William Gurnall.