Matthew Henry's Complete Bible Commentary
Verses 12—13
I. Silence is here recommended as an instance of true friendship, and a preservative of it, and therefore an evidence, 1. Of wisdom: A man of understanding, that has rule over his own spirit, if he be provoked, holds his peace, that he may neither give vent to his passion nor kindle the passion of others by any opprobrious language or peevish reflections. 2. Of sincerity: He that is of a faithful spirit, that is true, not only to his own promise, but to the interest of his friend, conceals every matter which, if divulged, may turn to the prejudice of his neighbour. MHBCC 640.14
II. This prudent friendly concealment is here opposed to two very bad vices of the tongue:—1. Speaking scornfully of a man to his face: He that is void of wisdom discovers his folly by this; he despises his neighbour, calls him Raca, and Thou fool, upon the least provocation, and tramples upon him as not worthy to be set with the dogs of his flock. He undervalues himself who thus undervalues one that is made of the same mould. 2. Speaking spitefully of a man behind his back: A tale-bearer, that carries all the stories he can pick up, true or false, from house to house, to make mischief and sow discord, reveals secrets which he has been entrusted with, and so breaks the laws, and forfeits all the privileges, of friendship and conversation. MHBCC 640.15