Matthew Henry and continuators on Proverbs 15:28

28 The heart of the righteous studieth to answer: but the mouth of the wicked poureth out evil things.

Here is, 1. A good man proved to be a wise man by this, that he governs his tongue well; he that does so the same is a perfect man, Jam. iii. 2. It is part of the character of a righteous man that being convinced of the account he must give of his words, and of the good and bad influence of them upon others, he makes conscience of speaking truly (it is his heart that answers, that is, he speaks as he thinks, and dares not do otherwise, he speaks the truth in his heart, Ps. xv. 2), and of speaking pertinently and profitably, and therefore he studies to answer, that his speech may be with grace, Neh. ii. 4; v. 7. 2. A wicked man is proved to be a fool by this, that he never heeds what he says, but his mouth pours out evil things, to the dishonour of God and religion, his own reproach, and the hurt of others. Doubtless that is an evil heart which thus overflows with evil.