*Minor differences ignored. Grouped by changes, with first version listed as example.
God here makes a provision for every man's character and good name, lest any should be undeservedly weighed down by calumnies and false accusations. The same synecdoche exists here, which I have pointed out in the previous Commandments, for God comprises many things under a single head. With reference to the words, inasmuch as d, gned, properly means a witness, it may be literally translated, "Thou shalt not answer a false witness against thy neighbor," but then the particle as must be supplied. The Hebrews poorly translate it in the vocative case, Thou shalt not speak, O false witness, etc. Although God seems only to prescribe that no one, for the purpose of injuring the innocent, should go into court, and publicly testify against him, yet it is plain that the faithful are prohibited from all false accusations, and not only such as are circulated in the streets, but those which are stirred in private houses and secret corners. For it would be absurd, when God has already shewn that men's fortunes are cared for by Him, that He should neglect their reputation, which is much more precious. In whatever way, therefore, we injure our neighbors by unjustly defaming them, we are accounted false witnesses before God. We must now pass on from the prohibitive to the affirmative precept: for it will not be enough for us to restrain our tongues from speaking evil, unless we are also kind and equitable towards our neighbors, and candid interpreters of their acts and words, and do not suffer them, as far as in us lies, to be burdened with false reproaches. Besides, God does not only forbid us to invent accusations against the innocent, but also to give currency to reproaches and sinister reports in malevolence or hatred. Such a person may perhaps deserve his ill-name, and we may truly lay such or such an accusation to his charge; but if the reproach be the ebullition of our anger, or the accusation proceed from ill-will, it will be vain for us to allege in excuse that we have advanced nothing but, what is true. For when Solomon says that "love covereth many sins;" whereas "hatred brings reproaches to light," [1] (Proverbs 10:12;) he signifies, as a faithful expositor of this precept, that we are only free from falsehood when the reputation of our neighbors suffers no damage from us; for, if the indulgence of evil-speaking violates charity, it is opposed to the Law of God. In short, we must conclude that by these words a restraint is laid on all virulence of language which tends to bring disgrace on our brethren; and on all petulance also, whereby their good name suffers injury; and on all detractions, which flow from malice, or envy, and rivalry, or any other improper feeling. We must also go further, and not be suspicious or too curious in observing the defects of others; for such eager inquisitiveness betrays malevolence, or at any rate an evil disposition. For, if love is not suspicious, he who condemns his neighbor either falsely, or upon trifling surmises, or who holds him in light esteem, is undoubtedly a transgressor of this Commandment. Consequently, we must close our ears against false and evil speaking; since he is just as injurious to his brother who eagerly listens to sinister reports respecting him, as he who exercises his tongue in maligning him. The necessity of this instruction let each man estimate by his own disposition; for scarcely one in a hundred will be found who will be as kind in sparing the character of others, as he himself desires to be pardoned for manifest vices; nay, slander is often praised under the pretext of zeal and conscientiousness. Hence it happens that this vice insinuates itself even among the saints, creeping in under the name of virtue. Moreover, the volubility of the tongue causes us to think it a light transgression to inflict a deadly and disgraceful wound on our brother, to whom, nevertheless, his good name is of more importance than his life. The sum is, that we should manifest our charity no less by candor, and by abstaining from slander, than by the performance of other duties.
1 - "Hatred stirreth up strifes; but love covereth all sins." -- A.V. The latter clause, in C.'s quotation, is probably rather intended to be the necessary converse of the latter part of the proverb than a paraphrastic rendering of the first, which it does not appear that the words will bear.
Neither shalt thou bear false witness against thy neighbour - Have you not been guilty of evil - speaking? Of needlessly repeating the real fault of your neighbour? If I see a man do an evil thing, and tell it to another, unless from a full and clear conviction, that it is necessary to mention it just then, for the glory of God, the safety or good of some other person, or for the benefit of him that hath done amiss; and unless I then do it only so far, as is necessary to these ends, that is evil - speaking. O beware of this! It is scattering abroad arrows, fire - brands, and death.
*More commentary available at chapter level.