Many years ago, as a young christian, I attended a church where the preacher told me that mental illness is from the devil. He quoted to me II Timothy 1:7, "For God hath not given us the spirit of fear; but of power, and of love, and of a sound mind." He stated that if God gave us a "sound mind", then who was it that gave us a "troubled mind"?...it had to be Satan. I trusted this preacher and from then on believed that any mental illness came from the devil. This also meant that the person who had the illness must have sinned. It just made sense to me that sinfulness and mental illness went together.
During this same time, I learned that mental illness and the taking of medications for it were sinful. There was no reason to take medications because if you just got right with God, then you wouldn't have any mental problems. Taking medicine was almost like doing drugs. It would alter your mind and make you susceptible to more satanic influence. Since mental illness was from the devil, then medications for it must also be from the devil. Even that made sense to me.
I heard the lessons about the demoniac(s) of Gadara found in Matthew 8, Mark 5, and Luke 8. These guys were possessed with devils. One guy was so tormented by them that the book of Mark describes him in grim detail. This guy definitely had mental illness, and he was possessed by a legion of demons. There is no greater "proof text" used to prove that mental illness comes from the devil. Especially since this man was delivered from his torment as soon as he "trusted in Jesus". The devils were cast out and there was peace.
This is what was taught to me and this what I believed for many, many years. I became very judgmental of anyone who had mental problems. They would be fine if they would only confess their sins and turn from them. I just knew that God would instantly heal them the same way he did when he delivered the demoniac of Gadara.
Join me again next time to read about what I learned many years later.