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

Jamieson-Fausset-Brown Bible Commentary

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).

Matthew Henry's Concise Commentary

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.