John Gill Commentary Proverbs 12:23

"A prudent man concealeth knowledge; But the heart of fools proclaimeth foolishness." — Proverbs 12:23 (ASV)

A prudent man conceals knowledge
Of things natural or divine, which he is furnished with; not but that he is willing to communicate it, as he should, at proper times, in proper places, and to proper persons; but he does not needlessly and unseasonably speak of it; he does not make a show of it, or boast and brag of it: he modestly forbears to speak of what he knows, but when there is a necessity for it, even of that which may be lawfully divulged; which is a point of prudence and modesty; otherwise it is criminal to reveal secrets, or publish what should be kept private or should not be known.

Aben Ezra interprets it of a wise man's hiding his knowledge in his heart, that he may not forget it; but the heart of fools proclaims foolishness ;
that which they have in their hearts and minds, and which they take for deep knowledge, profound and recondite learning, they proclaim with their mouths in a noisy and clamorous way; and while they declare their ill shaped notions, their incoherent and unconnected ideas of things, they betray their ignorance and folly, as ostentatious men do.