Jeremiah 23:29

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.

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.