Evil spirits are not only able to inject thoughts into the believer’s mind, but they can also form different kinds of pictures in his mind. Some of these pictures are very clean and good, which the believer likes. But some are very filthy and sinful and are abhorred by the believer’s conscience. Whether it is something good or bad, something the believer likes or abhors, he has no power to stop these pictures from coming into his own mind. Past experiences, future predictions, and many other things are always lingering before his eyes in spite of the opposition of his will. The believer’s imagination has fallen into passivity; he can no longer control his own imagination and has yielded to evil spirits who are now using his imagination at will. A believer should realize that everything that is not produced by his own mind is given to him by supernatural spirits.
Some dreams are natural, but some are supernatural. Some belong to God, and some belong to the devil. Except for the dreams that are caused by man’s own physiology or mind, the rest are supernatural. If a believer’s mind is open to evil spirits, many of his dreams at night are probably the "pictures" he obtained during the day in disguise. Evil spirits make him see the pictures during the day and dream about them at night. If a believer wants to check if his dream is from evil spirits, he only needs to ask, "Has my mind been passive during the day?" If so, the dream which he receives is not trustworthy. Dreams from God always make people normal, peaceful, stable, reasonable, and sensible. But dreams that come from evil spirits are all strange, vain, false, foolish, and cause people to become elated, stupefied, confused, and irrational.
The evil spirits can give a believer many strange dreams, some of which are very good, because his mind is passive. If a believer’s mind has fallen into passivity, all of his dreams will not be from God, neither will they be natural; instead, they will be from evil spirits. At night the mind is naturally not as active as during the day, and it becomes more passive. Then evil spirits will seize the opportunity to accomplish their goal. These kinds of dreams at night make the believer dizzy and dampen his spirit when he wakes up in the morning. Sleep does not seem to increase his vigor, because while he is sleeping, evil spirits are affecting his whole being through the passive mind. All who frequently suffer from dreams at night have evil spirits working in their mind. If a believer single-mindedly rejects the evil spirits’ work both during the day and night, he will soon be free.
Insomnia is a very common disease among today’s believers. It is the most obvious evidence of evil spirits’ work in the mind. When many believers lay on the bed at night, many thoughts pour into their mind. They are continuously thinking about their work in the day, recalling their past experiences, or reviewing many unrelated things through their mind. It appears as if they are "thinking" about thousands of things and considering what they should do, how they should do it, and what is the best strategy. It appears as if they are considering in advance the things that have to be done the next day, what they should plan, what kind of circumstances they will encounter, and how they should deal with different problems. These thoughts come repeatedly. Although the believer knows that the bed is the place for sleep, and that it is not a desk where one does his thinking, the mind keeps on turning. Although the believer knows how important sleep is to his work the next day, and that he desperately needs to sleep and does not want to think, he cannot do as he pleases for reasons unknown to him. His mind continues to vigorously work and hinder his sleep. Perhaps the believer has tasted the bitterness of insomnia for many days. Perhaps he has completely rested from every kind of work and does not want to use his mind anymore. However, when night comes, even though he is very tired, the mind will not rest, as if it is a "thinking machine" which is very active and refuses to stop. His own will has absolutely no power over his own thoughts; he can only let it stop by itself. The believer cannot stop his thoughts. Before his mind can rest and he can go to sleep, he can only wait for a certain kind of power within himself to stop him from thinking. Sleep should refresh people. But after a person continuously has this kind of experience for several nights, he will regard sleeping, bed, and the night as something dreadful. Nevertheless, he cannot afford not to sleep. Every morning when he rises up, it seems as if he has just come back from a horrible world. The head is confused, the will is paralyzed, and all of his strength seems to have disappeared.
At such times, the believer always considers his body the cause of these phenomena. He may think that he is mentally disturbed or that he has overworked his mind. Actually: (1) These reasons are hypothetical most of the time and not real. (2) Even if reasons do exist, the believer should be cured once he rests or is remedied by some natural methods. Yet commonly-used natural methods often turn out to be ineffective. (3) These reasons are the signboards that evil spirits use to disguise their work in secret. When thoughts are racing in the believer’s mind at night, he should ask himself, "Where do these thoughts come from? Are they my thoughts? I do not want these thoughts, and I have no intention to have these thoughts. How then can I say that they are my thoughts? If they are not my thoughts, who is giving me so many confused, defiled, and depressing thoughts? Who else is there, other than evil spirits?"
(Collected Works of Watchman Nee, The (Set 1) Vol. 14: The Spiritual Man (3), Chapter 2, by Watchman Nee)