John Calvin on Colossians 4:6

6. Your speech. He requires suavity of speech, such as may allure the hearers by its profitableness, for he does not merely condemn communications that are openly wicked or impious, but also such as are worthless and idle. Hence he would have them seasoned with salt. Profane men have their seasonings of discourse, Sales. The term is frequently employed by classical writers to denote witticisms. See Cic. Fam. 9:15; Juv. 9:11; Hor. Ep. 2:2, 60. — Ed. but he does not speak of them; nay more, as witticisms are insinuating, and for the most part procure favor, “Et que par ce moyen il seroit a craindre que les fideles ne s’y addonassent;” — “And as on this account it was to be feared that believers would addict themselves to this.” he indirectly prohibits believers from the practice and familiar use of them. For he reckons as tasteless everything that does not edify. The term grace is employed in the same sense, so as to be opposed to talkativeness, taunts, and all sorts of trifles which are either injurious or vain. “Ou s’en vont en fumee;” — “Or vanish into smoke.”

That ye may know how. The man who has accustomed himself to caution in his communications will not fall into many absurdities, into which talkative and prating persons fall into from time to time, but, by constant practice, will acquire for himself expertness in making proper and suitable replies; as, on the other hand, it must necessarily happen, that silly talkers expose themselves to derision whenever they are interrogated as to anything; and in this they pay the just punishment of their silly talkativeness. Nor does he merely say what, but also how, and not to all indiscriminately, but to every one. For this is not the least important part of prudence — to have due regard to individuals. “Car c’est des principales parties de vraye prudence, de scauoir discerner les personnes pour parler aux vns et aux autres comme il est de besoin;” — “For it is one of the chief departments of true prudence, to know how to discriminate as to individuals, in speaking to one and to another, as there may be occasion.”