John Calvin - The ninth commandment, in its negative and positive charges

Thou shalt not bear false witness against thy neighbour.

... And yet it is strange, with what supine security men everywhere sin in this respect [that we, by calumnies and false accusations, injure our neighbour's name, or by falsehood impair his fortunes; in fine, that we injure any one from petulance, or a love of evil-speaking (2.8.47)]. Indeed, very few are found who do not notoriously labour under this disease: such is the envenomed delight we take both in prying into and exposing our neighbour's faults. Let us not imagine it is a sufficient excuse to say that on many occasions our statements are not false. He who forbids us to defame our neighbour's reputation by falsehood, desires us to keep it untarnished in so far as truth will permit. Though the commandment is only directed against falsehood, it intimates that the preservation of our neighbour's good name is recommended. It ought to be a sufficient inducement to us to guard our neighbour's good name, that God takes an interest in it. Wherefore, evil-speaking in general is undoubtedly condemned. Moreover, by evil-speaking, we understand not the rebuke which is administered with a view of correcting; not accusation or judicial decision, by which evil is sought to be remedied; not public censure, which tends to strike terror into other offenders; not the disclosure made to those whose safety depends on being forewarned, lest unawares they should be brought into danger, but the odious crimination which springs from a malicious and petulant love of slander. Nay, the commandment extends so far as to include that scurrilous affected urbanity, instinct with invective, by which the failings of others, under an appearance of sportiveness, are bitterly assailed, as some are wont to do, who court the praise of wit, though it should call forth a blush, or inflict a bitter pang. By petulance of this description, our brethren are sometimes grievously wounded. But if we turn our eye to the Lawgiver, whose just authority extends over the ears and the mind, as well as the tongue, we cannot fail to perceive that eagerness to listen to slander, and an unbecoming proneness to censorious judgements are here forbidden. It were absurd to suppose that God hates the disease of evil-speaking in the tongue, and yet disapproves not of its malignity in the mind. Wherefore, if the true fear and love of God dwell in us, we must endeavour, as far as is lawful and expedient, and as far as charity admits, neither to listen nor give utterance to bitter and acrimonious charges, nor rashly entertain sinister suspicions. As just interpreters of the words and the actions of other men, let us candidly maintain the honour due to them by our judgement, our ear, and our tongue.

- John Calvin (Institutes of the Christian Religion, 2.8.48)