Jeremiah 23:29

[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.