Jeremiah 23:29 (NKJV)
When people build roads they often have to remove or break up rocks that are in the way of the road that is being built. In the past, there would often be crews of men using sledgehammers to break up the rocks, but today there are machines that can do the work that in the past was done through manual labor. For some jobs, sledgehammers or hydraulic jackhammers are used to break up the rocks. But, whether it is modern machinery or just a simple hammer, one thing that has always been true is that it can take a while to break up the rocks that need to be removed.
In Jeremiah 23, God's Word is compared to a fire and a hammer. The truth of the Word will help to burn up the things in our life that are wrong by showing us those things and giving us guidelines as to what we should do. God's Word is like a hammer in that through continual use of it in our life it will help us break down areas that may have been hard to deal with. Through God's Word, the Holy Spirit will give us direction and wisdom on how to apply the Word to our life to burn up and break down things that need to be removed. Jesus said that we would know the truth and the truth would make us free (John 8:32), but this may not happen immediately or overnight.
Another way that God's Word is like a fire or a hammer is when we take a stand in faith on God's Word. Just like it may take a fire some time to burn up some things and it make take a longer period of time for a hammer to break up a rock, depending on its size, God's Word will work in our life to burn up and break down the problems we face and help us remove the things that would hinder us from doing God's will. We need to keep the fire of the Word burning and keep hammering the situations in our life with God's Word. As we keep standing on the Word and speaking the Word it will make a difference in us and in our life.