"The fool has said in his heart, “There is no God.” They are corrupt. They have done abominable deeds. There is no one who does good." Psalm 14:1 WEB
This is not about that one who is unsure. That person still has debate within their mind. Your mind does not defile you because it is an area in which the devil can plant thoughts. All thoughts are not our own.
With that said Satan cannot read your mind because he isn't all-knowing like God. He does not know your innermost thought until it comes out of your mouth. Then he can try to use it against you. Sinful thoughts are not a sin unless acted upon. This is why you should not say/do everything you think. That is when corruption comes.
Some people think they are good because they have done no bad. Bible says no one does good. The only good man was Jesus Christ. Our goodness is not God seeing us but Him seeing Christ in us. Don't be no fool.
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