The following Spurgeon quotation is from "Fathers in Christ," a sermon he preached Sunday Morning, 18 November 1883, at the Metropolitan Tabernacle. I include it here because it seems most applicable to the spirit of our age, which is terribly afraid of condemning even the most destructive and damning errors as "heresy."
"There used to be a company in the north of Scotland called "The Men." Why, if heresy had been preached before them, they would have been as provoked as Janet Geddes when she threw her cutty stool at the head of the preacher. They would not have endured these modern heresies as the present effeminate generation is enduring them.
Let the new theologians have liberty to preach what they like on their own ground, but not in our pulpits. Alas! the leading members in many churches are Christians without backbones, molluscous, spongy; snails I would call them, only they have not the consistency of a snail’s shell. They are ready to swallow any mortal thing if the preacher seems clever and eloquent.
Cleverness and eloquence—away with them forever! If it is not the truth of God, the more cleverly and eloquently it is preached the more damnable it is. We must have the truth and nothing but the truth, and I charge the fathers in Christ all over England and America to see to this. Get ye to your watchtower and guard the flock, lest the sheep be destroyed while they are asleep." ~ Charles H. Spurgeon