What do fire and a hammer have in common? First, both have an effect of changing what they touch, don't they? Nothing touched by fire is quite the same - so it is with the hammer - they both can reduce to pieces that which are touched by their influence. Second, there is a "heating" effect of both. The hammer begins to "heat up" the nail as it drives it through the wood - repeated blows from the hammer actually change the temperature of the nail! So, there are some commonalities between the hammer and fire. Why on earth does God compare his Word to fire or a hammer? Perhaps it is for the reasons we have just stated - it changes what it comes into contact with and it has a way of changing the "temperature" of whatever it touches.
Is not My word like fire [that consumes all that cannot endure the test]? says the Lord, and like a hammer that breaks in pieces the rock [of most stubborn resistance]? (Jeremiah 23:29 AMP)
It is important to see God does not say the purpose of the fire is to consume us and get us all ashy - it is just to consume whatever cannot hold up to the test of the heat! So, in other words, whenever we feel like the Word of God is a little "consuming" in its focus, it is like a farmer doing a controlled burn around his place. The purpose of the controlled burn is to remove the weeds and brush which threaten the potential for his harvest! The Word of God is really not after the good stuff - it is after the "chaff" - the unfruitful, unproductive, and choking influences of our life. Have you noticed how well some of the wood burns in a fire, while the other wood seems to be harder to "catch" and it burns a lot longer before it is reduced to ash. The "hardness" of the wood is often the determining factor of how long the fire has to "work" upon the wood to achieve the optimal effect of reducing the wood. Sometimes our heart is responsive to the fire of God's Word, allowing the Word to take hold quite quickly. Other times, it is a little harder, isn't it?
The likeness of the Word of God to a hammer is pictured here not so much as the hammer driving home the nail, but of pounding upon rock. I think this is an appropriate picture of our hearts sometimes - rocky, hard, and just needing a little "pounding". My dad used to have a couple of sledge hammers - some smaller like hammer size, others bigger like the size of an ax. It took quite a bit of effort to wield the sledge hammer, regardless of the size. Why? They carried some "weight" to them - because what they would come into contact with was often unyielding and requires a little more force to affect the desired change. If we had an unyielding stone in the garden, dad could take a couple of cracks of the sledge hammer against the stone, effectively breaking it apart into "manageable" sizes. Then he could remove them one by one. I think God's Word is sometimes like this in our lives - it encounters some pretty unyielding stones and must break those stones up into smaller pieces, allowing for those pieces to be removed and discarded in order to begin to prepare the place it occupied for fresh growth.
The hammer on the stone produces some "heat" with each blow. It is perhaps the influence of this "heat" which gets the stone to the point of beginning to yield to the blows. A sledge hammer applies force - it is the force which begins the process of changing the consistency of what it touches. If you know anything about using a sledge hammer, you know it is the weight of the hammer which is used to produce the force. God's Word is a "weighty" thing in his hand! It is by the strength of his hand and the force of his Word we are changed - our places of our most stubborn resistance are broken into manageable pieces until they no longer find a suitable place of dwelling in us any longer.
Fire or hammer - either way, the effects are similar. The Word embraced becomes the basis of change. Embrace it quickly and we see the effect of its influence almost immediately in our lives. Exert a little stubborn resistance to its influence and we might just need a little more heat or a few more blows. Just sayin!