Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Heareth - The verb of the second clause is inserted in the first, just as in the next verse that of the first is inserted in the second. Stress is laid upon the obstinacy of the scorner who refuses to hear, not only "instruction," but also the much stronger "rebuke."
The fruit of his mouth - Speech rightly used is itself good, and must therefore bring good fruit.
Eat violence - i. e., Bring upon itself repayment in kind for its deeds of evil.
Compare Pro 11:24. There is a seeming wealth behind which there lies a deep spiritual poverty and wretchedness. There is a poverty which makes a person rich for the kingdom of God.
On the one side is the seeming advantage of wealth. The rich man who gets out of many troubles often escapes from a just retribution by his money. But then the poor man in his turn is free from the risk of the threats and litigation that beset the rich. He "hears no rebuke" (the words are not used as in Pro 13:1) just as the dead "hear not the voice of the oppressor" Job 3:18 or the abuse of the envious.
Very beautiful in its poetry is the idea of the light "rejoicing" in its brightness (compare Psa 19:5; Job 38:7). Note also the distinction between the "light" and the "lamp." The righteous ones have the true light in them. That which belongs to the wicked is only derived and temporary, and even that shall be extinguished before long. Compare a like distinction in Joh 1:8; Joh 5:35.
Either:
(1) "By pride alone comes contention" - that is the one unfailing spring of quarrels; or
(2) "By pride comes contention only" - it, and it alone, is the fruit of pride.
By vanity - literally, "by a breath," i. e., by a windfall, or sudden stroke of fortune, not by honest labor. The general meaning seems to be that the mere possession of riches is as nothing; they come and go, but the power to gain by skill of hand ("labor") is everything.
When the desire cometh - The desire comes, it is a tree of life: i. e., the object of our desires is attained. Compare Pro 3:18.
Hard - The primary meaning of the original word is permanence (compare Deu 21:4; Mic 6:2). This may be applied as here to the hard dry rock, to running streams, or to stagnant pools. In either case, the idea is that of the barren dry soil, or the impassable marsh, in contrast with the fountain of life, carrying joy and refreshment with it.
The connection is somewhat obscure. Either, "Satisfied desire is pleasant, therefore it is an abomination to fools to depart from the evil on which their minds are set;" or, "Sweet is the satisfaction of desire, yet the wicked will not depart from the evil which makes that satisfaction impossible."
An expression of trust, that in the long run the anomalies of the world are rendered even (compare the marginal references). The heaped up treasures of the wicked find their way at last into the hands of better men.
The contrast is the ever recurring one between honest poverty and dishonest wealth. "The new-plowed field of the poor is much food, but there are those, who, though rich, perish through their disregard of right."