John Gill, on Prov 15:28

The heart of the righteous studieth to answer,.... He thinks before he speaks, meditates what he shall say, what answer to give to men; whether in things civil, natural, or religious; and what to return to the Lord when he is reproved by him; or what to say in prayer to him, or by way of thankfulness for mercies received from him; see Pro 3:6; though our Lord advises his disciples, when summoned before their persecutors, not to meditate beforehand what they should answer, since they should have immediate assistance, Luk 21:14; but this was in extraordinary cases; in common ones the observation of the wise man should be attended to. A Jewish (u) writer renders the words, "the heart of the righteous meditates wormwood", or bitter things; see Pro 5:4; as the judgment of God, death, and hell; this sense is mentioned by Aben Ezra, but rejected; but the mouth of the wicked poureth out evil things; without any previous thought and consideration, without fear or wit; in great abundance, as water out of a fountain; thus an evil man out of the evil treasure of his heart brings forth evil things readily and at once, having no concern about the consequences of things, Mat 12:25; See Gill on Pro 15:2. (u) Kabvenaki.