"One bright benison which private prayer brings down upon the ministry is an indescribable and inimitable something, better understood than named; it is a dew form the Lord, a divine presence which you will recognize at once when I say it is 'an unction from the Holy One." What is it? I wonder how long we might beat our brains before we could plainly put into words what is meant by preaching with unction; yet he who preaches knows its presence, and he who hears soon detects its absence; Samaria in famine, typifies a discourse without it; Jerusalem, with her feasts of fat things full of marrow, may represent a sermon enriched with it. Everyone one knows what the freshness of the morning is when orient pearls abound on every blade of grass, but who describe it, must less produce if of itself? Such is the mystery of spiritual anointing; we know, but we cannot tell to others what it is. It is as easy as it is foolish to counterfeit it, as some do who use expressions which are meant to betoken fervent love, but oftener indicate sickly sentimentalism or mere cant. "Dear Lord!" "Sweet Jesus!" "Precious Christ" are by them poured out wholesale, till one is nauseated, if not profane.
Some have tried to imitate unction by unnatural tones and whines; by turning up their eyes, and lifting their hands in a most ridiculous manner. . . Certain brethren aim at inspiration through exertion and loud shouting, but it does not come. . . 'To affect feeling,' says Richard Cecil, 'is nauseous and soon detected, but to feel is the is the readiest way to the hearts of others.' Unction is a thing which you cannot manufacture, and its counterfeits are worse than worthless; yet it is in itself priceless, and beyond measure needful if you would edify believers and bring sinners to Jesus. To the secret pleader with God this secret is committed; upon him rests the dew of the Lord, about him is the perfume which makes glad the heart. If the anointing we bear come not from the Lord of hosts we are deceivers, and since only in prayer can we obtain it, let us continue instant, constant, fervent in supplication. Let the fleece lie on the threshing-floor of supplication till it is wet with the dew of heaven. Go not to minister in the temple till you have washed in the laver. Think not to be a messenger of grace to others till you have seen the God of grace for yourselves, and had the word from his mouth."
--Charles Spurgeon, Lectures To My Students, 50.