You are of your father the devil, and your will is to do your father's desires. He was a murderer from the beginning, and has nothing to do with the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies. -- John 8:44
This is seen even more clearly when we think about what demons are like. They are unholy: anything that they experience, cannot be a holy experience. The devil is perfectly wicked. “You belong to your father, the devil, and you want to carry out your father’s desire. He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies.” (John 8:44) “He who does what is sinful is of the devil, because the devil has been sinning from the beginning.” (1John 3:8) Therefore the demons are called evil spirits, unclean spirits, powers of darkness, and so on. “For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms.” (Eph 6:12)So it is plain that anything in the minds of demons cannot be holy, or lead to true holiness by itself. The demons clearly know many things about God and religion, but they do not have a holy knowledge. The things they know in their minds may make impressions in their hearts— indeed we do see that the demons have very strong feelings about God; so strong, in fact, that they “shudder.” But they are not holy feelings because they have nothing to do with the work of the Holy Spirit. If this is true of the experience of demons, it is also true of the experience of men.Notice this, that it does not matter how genuine, sincere, and powerful these thoughts and feelings are. Demons, being spiritual creatures, know God in a way that men on earth cannot. Their knowledge of God’s existence is more concrete than any man’s knowledge could be. Because they are locked in battle with the forces of good, they have a sincerity of knowledge as well. On one occasion Jesus cast out some demons. “What do you want with us, Son of God?” they shouted. “Have you come here to torture us before the appointed time?” (Mat 8:29) What could possibly be a more clear-cut experience than this? However, while their thoughts and feelings are genuine and powerful, they are not holy.Also we can see that the holy objects of their thoughts doesn’t make their thoughts and feelings holy. The demons know God exists! Matthew 8:29 shows they know more about Jesus than many people do! They are thoroughly that Jesus will judge them some day, because He is holy. But it is clear that genuine, sincere, and powerful thoughts and feelings about holy, spiritual things, is no proof of God’s grace in the heart. Demons have these things, and look forward to eternal punishment in hell. If men have no more than what the demons have, they will suffer in the same way.