The kind of tongue you have is determined by the kind of words rolling off it regularly. If your tongue is regularly used for dirty slangs, worldly music, abusive words and the like, the devil marks it as his. If that same tongue now turns around to cast out demons, they would only have a good laugh at its expense because a house divided against itself cannot stand (Mark 3:25). A tongue that belongs to the devil cannot cast him out.

“And He called them unto Him, and said unto them in parables, How can Satan cast out Satan.
Mark 3:23

In Mark 3:22-27 when the people accused Jesus of casting demons out with the power of the devil. He said that was impossible because Satan cannot cast himself out. In other words, as powerful a weapon as your tongue is, if it is of the devil, it cannot work against him. Now you see why people use the word of God in certain situations to no effect. Many people pray in the name of Jesus, but He does not show up for them because He shows His own. It is good to prophesy, it is good to make confessions, but the power of your prophecy is determined by the owner of your tongue.

On the other hand, if your tongue is used to preach the gospel, if the word of God regularly comes out of your month, if you use words that are seasoned with salt and avoid dirty language, then God marks your tongue as His. He touches that tongue with a coal of fire and every word that comes out of it will come out with power. Then you can command demons and they will obey; you can speak to situations and they will do what you say. Matthew 18:18 says:
“Verily I say unto you, whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven.”
Written by Pastor E.A. Adeboye.