When the devil in the form of a serpent tempted Eve in the Garden of Eden what did he do? Didn't he tell her truth? "He said unto the woman, Yea, hath God said, Ye shall not eat of every tree of the garden?" Genesis 3:1. This was all true. No error here. And Eve concurred with the devil by saying, "We may eat of the fruit of the trees of the garden: But of the fruit of the tree which is in the midst of the garden, God hath said, Ye shall not eat of it, neither shall ye touch it, lest ye die." Genesis 3:2, 3
Then what did the devil say? He said: "Ye shall not surely die: For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil." Genesis 3:4, 5. Truth again, except for the first five words. But the truth convinced Eve to believe the lie!
What did the devil do? He mixed truth with error. Why? Because he knew that you can't deceive intelligent beings into believing error by giving them 100% error. They won't fall for it. So you give them truth, lots of it, to win their confidence. Then you bring in just enough error to get them to fall for it. Once they have fallen for it, then it is safe to give them more. But your whole motive is to deceive them into believing error, so at first you give them only a little.
Isaiah warned us of this when he said: "And when they shall say unto you, Seek unto them that have familiar spirits, and unto wizards that peep, and that mutter: should not a people seek unto their God? for the living to the dead? To the law and to the testimony: if they speak not according to this word, it is because there is no light in them." Isaiah 8:19, 20. So many say, "But there is light and truth in it. Shouldn't we take the truth and ignore the error?" NO! I wondered about this for years myself but now I see why Isaiah said what he said. Yes, there may be truth found in the error. In fact, there will always be truth mixed error. That is how we are deceived into believing error. The truth is put there as a means to deceive you and for that very reason it all becomes error. If you are looking for truth, go to the sources that you can be confident are all truth. God's word. Only when you are well grounded in God's word should you ever look at what men have to say. The devil will use even the best of them to lead us astray. John Harvey Kellogg, A. F. Ballenger, and A. T. Jones are only a few.
When truth is used to deceive someone into believing error it all becomes error. That's what Isaiah is telling us. When truth is used to deceive, it is no longer truth but 100% error. We should have nothing to do with any of it. It is darkness! We should run from it as fast as we can. Trying to separate truth from error is exactly what the devil wants us to do. He knows there is a very good chance he will get us if we do. Why? Because there's another truth that says "By beholding we become changed." The devil is a genius at disguising error and making it appear very compelling. The more educated and self-assured one is, the greater the devil's success at getting them. Why? Because they have already fallen for his deception that they are smart enough to discern his lie from the truth. He knows it is only time until they fall for even more of his deceptions.
The devil's deceptions will become so compelling that we are told that if it were possible, even the elect would be seduced. (Mark 13:22). Before one becomes self-confident, a study of who the elect are and why they will not be deceived needs to be undertaken.
2 Timothy 2:15