Like as a fire - God's word is the great purifier which destroys all that is false and aves, only the genuine metal. Compare Hebrews 4:12.

Like a hammer ... - God's word rouses and strengthens the conscience and crushes within the heart everything that is evil.

Is not my word like as a fire? - It enlightens, warms, and penetrates every part. When it is communicated to the true prophet, it is like a fire shut up in his bones; he cannot retain it, he must publish it: and when published, it is like a hammer that breaks the rock in pieces; it is ever accompanied by a Divine power, that causes both sinner and saint to feel its weight and importance.

In the original words there is something singular: הלוא כה דברי כאש halo coh debari kaesh, "Is not thus my word like fire?" I suspect, with Dr. Blayney, that כה coh, thus, was formerly written כח coach, strength or power; and so it was understood by the Targumist: "Are not all my words strong, like fire?" and probably the author of the Epistle to the Hebrews read it thus, and had it in view when he wrote: "For the word of God is quick and powerful, and sharper than any two-edged sword," Hebrews 4:12. This admitted, the text would read, "Is not my word powerful, like fire?" or, "Is not the power of my word like fire?" But however we understand the words, let us take heed lest we think, as some have thought and affirmed, that the sacred writings are quite sufficient of themselves to enlighten, convince, and convert the soul, and that there is no need of the Holy Spirit. Fire itself must be applied by an agent in order to produce its effects; and surely the hammer cannot break the rock in pieces, unless wielded by an able workman. And it is God's Spirit alone that can thus apply it; for we find it frequently read and frequently spoken, without producing any salutary effects. And by this very thing the true preachers of the word of God may be distinguished from the false, non-commissioned ones; those who run, though they are not sent, Jeremiah 23:21. The word of him who has his commission from heaven shall be as a fire and as a hammer; sinners shall be convinced and converted to God by it. But the others, though they steal the word from their neighbor - borrow or pilfer a good sermon, yet they do not profit the people at all, because God did not send them, Jeremiah 23:32; for the power of God does not in their ministry accompany the word.

There may be an allusion to the practice in some mining countries, of roasting stones containing ore, before they are subjected to the hammer, in order to pulverize them. In Cornwall I have seen them roast the tin stones in the fire, before they placed them under the action of the hammers in the stamp mill. The fire separated the arsenic from the ore, and then they were easily reduced to powder by the hammers of the mill; afterwards, washing the mass with water, the grains of tin sank to the bottom, while the lighter parts went off with the water, and thus the metal was procured clean and pure. If this be the allusion, it is very appropriate.

Is not my word like as a fire? saith the Lord,.... The legal part of it is as fire; it is called a "fiery law", Deuteronomy 33:2; like fire, it is quick and piercing, and penetrating into the hearts and consciences of men; and works wrath there, and raises a fearful expectation of fiery indignation; it threatens with everlasting fire; it sentences men to the fire of hell; and the righteous Judge, in the execution of it, will be a consuming fire to wicked men. The Gospel part of the word is like fire, on account of the light the entrance of it gives to sinners; by which they see their own impurity, impotence, and the insufficiency of their own righteousness, and the way of life and salvation by Christ; and by the light of this fire saints are directed in their walk and conversation; and by it immoralities, errors, and superstition, are detected: also on account of the heat of it; it is the means of a vital heat to sinners, the savour of life to them; and is warming and comforting to saints, and causes their hearts to burn within them; it inflames them with love to God, Christ, and one another, and with zeal for truth and the interest of a Redeemer; though it has a scorching and tormenting heat to wicked men, and fills them with burning malice and envy, Revelation 11:5; and, through the corruption of human nature, is the occasion of contention and discord, for which reason Christ calls it fire, Luke 12:49; and indeed it has different effects on different objects, as fire, which hardens some things and softens others; see 2 Corinthians 2:16; moreover, it may be compared to fire for its purifying, separating, and trying nature: as fire purifies gold and silver, and separates the dross, and tries the metal, and shows it what it is; so the Gospel tries men's principles, and discovers what they are, and separates one from another: and also for its consuming nature; it opposes, weakens, and burns up the worst in man, his lusts and corruptions, which it teaches him to deny; and the best in man, all his holiness and righteousness he depended upon; and it burns up the chaff of false doctrine and human inventions before mentioned.

and like a hammer that breaketh the rock in pieces? to which the heart of man may be compared, being hardened by sin, confirmed in it; destitute of spiritual life; stupid and senseless; stubborn and inflexible; on which no impressions are made, and is impenitent and inflexible; see Zechariah 7:12; now the word of the Lord, in the hand of the Spirit, is a means of breaking such hard hearts, and taking away the Obduracy and hardness of them; there is a legal contrition of it, through the law part of the word, by which there is a knowledge of sin, and the soul is wounded with a sense of it, and sore broken, but without any view of pardon, righteousness, and salvation by Christ; and there is an evangelical contrition or brokenness of heart, through the Gospel part of the word, by means of which the stony heart is not only broken, but melted and dissolved into true evangelical repentance for sin, through the discoveries of a Saviour bruised and broken for its sin, and through a view of free and full pardon by his blood, and justification by his righteousness. Now the word is only an instrument; it is not the efficient cause of all this; as a hammer is but an instrument, and a passive one, can do nothing of itself; it must be taken up and used by a powerful hand, or it can do no execution; what is a hammer without a hand? so the Gospel is only an instrument in the hand of, he Lord; but when he takes it into his own hand, and strikes with it, it will break the hardest heart in pieces, and make a stony heart a heart of flesh, Ezekiel 36:26.

Is not my word like as a fire? saith the LORD; and like a hammer that breaketh the rock in pieces?

29. As the "fire" consumes the "chaff," [Jer 23:28], so "My word" will consume the false prophets (Mt 3:12; Heb 4:12). "My word" which is "wheat" [Jer 23:28], that is, food to the true prophet and his hearers, is a consuming "fire," and a crushing "hammer" (Mt 21:44) to false prophets and their followers (2Co 2:16). The Word of the false prophets may be known by its promising men peace in sin. "My word," on the contrary, burns and breaks the hard-hearted (Jer 20:9). The "hammer" symbolizes destructive power (Jer 50:23; Na 2:1, Margin).

23:23-32 Men cannot be hidden from God's all-seeing eye. Will they never see what judgments they prepare for themselves? Let them consider what a vast difference there is between these prophecies and those delivered by the true prophets of the Lord. Let them not call their foolish dreams Divine oracles. The promises of peace these prophets make are no more to be compared to God's promises than chaff to wheat. The unhumbled heart of man is like a rock; if not melted by the word of God as a fire, it will be broken to pieces by it as a hammer. How can they be long safe, or at all easy, who have a God of almighty power against them? The word of God is no smooth, lulling, deceitful message. And by its faithfulness it may certainly be distinguished from false doctrines.