Albert Barnes Commentary Jeremiah 23:29

"Is not my word like fire? saith Jehovah; and like a hammer that breaketh the rock in pieces?" — Jeremiah 23:29 (ASV)

Like a fire – God’s word is the great purifier which destroys all that is false and proves only the genuine metal. .

Like a hammer … – God’s word rouses and strengthens the conscience and crushes within the heart everything that is evil.