A brother once told me he was suffering from impure thoughts. He used to hear voices in his head telling him God did not exist. Another person also told me he was always being assailed with negative thoughts of suicide.
There is no voice without a person. The devil is always trying to seize the command center of the body, the mind, because it gives the final approval for every action. Scripture admonishes us to cast down evil imaginations and thoughts.
Jeremiah 4:14 states, “O Jerusalem, wash thine heart from wickedness, that thou mayest be saved. How long shall thy vain thoughts lodge within thee?”
God described the people of Jerusalem as people with vain thoughts. What is in your heart or spirit manifests as a thought. Jesus said an evil man out of the evil treasure of his heart brings forth evil things. When your heart is clean, your thoughts will be clean.
How can you clean your heart or spirit? By washing it. How can you wash something that is invisible? The word of God can. Ephesians 5:26 reads, “That he might sanctify and cleanse it with the washing of water by the Word.”
When you read the Word everyday, it washes your heart clean and helps you to develop pure thoughts.