John Gill's Exposition of the Whole Bible
Proverbs 18:20
A man's belly shall be satisfied with the fruit of his mouth,.... With his own words and discourses, when they are prudent, pious, and savoury; when they are with grace, and minister it; they are satisfying to himself, to his own mind and conscience, and to his family; to all within his house, which is, as it were, his belly; but, if otherwise, it will not be profitable nor satisfying to either; and therefore, if a man would keep conscience easy, and be useful to others, he ought to take care what he says; see Proverbs 12:14;
[and] with the increase of his lips shall he be filled; the same thing as before, expressed in different words, alluding to the sowing, of seed in the earth, and the increase of it; as a man sows he reaps, and enjoys the fruits of his labour; according to what a man sows with his lips, such is his harvest he is afterwards a partaker of.