In the Bible, the word of God is described in a few different ways: it’s a sword, a hammer, and even a fire. The prophet Jeremiah had one of the tougher roles in the life of Israel, he is God’s mouthpiece leading up to and during the Babylonian exile.
It’s through the Israelites hypocrisy, injustice, and denial of God’s power that Jeremiah is ushered to say this in Jeremiah 5:14, “Because the people have spoken these words, I will make my words in your mouth a fire and these people the wood it consumes.”
In this context, God uses the analogy of fire to communicate the punishment due for disobeying him. If we don’t take God at his Word we’ll burn up like a fire.
Another way to look at this is that what God says will be accomplished. Like wood consumed by fire, we must fully absorb what God says or else it will absorb us. God will fulfill what he sets out to do. Not one of his words will fall to the ground, nor will any go out void. When we don’t recognize our sin, we fuel this fire. We will break unless we bow before Him.