The flesh is always the place where evil spirits work. If the mind is not renewed, even if a person is regenerated in his spirit, evil spirits will still have a chance to work. Even though the minds of many believers were turned for a moment at the time of their repentance, it does not mean that their eyes, which have been blinded by Satan, were completely enlightened. Perhaps many areas are still "veiled." Because these dark places were the working ground for evil spirits in past days, the fact that they are diminished today does not mean that they are altogether annihilated. Evil spirits still occupy these areas, from which they also direct their operations. It is very common to see evil spirits occupying the minds of men through sin. This happens before they are saved or even after they are saved. Even though some changes have taken place, the old ground has not been uncovered or removed. Therefore, evil spirits still occupy them as their base of operations.
Evil spirits are very careful in covering up their works. If a believer is fleshly, they will generate many thoughts through his mind which are similar to his character and condition. They will make him believe that these are his own thoughts and that they are natural. If such a person is seeking for the baptism of the Holy Spirit, they will counterfeit the work of the Holy Spirit and give him many supernatural revelations, convincing him that these are from God. Because evil spirits know that this kind of unrenewed mind is the best ground for their work, they obstruct the believer in many ways, causing him to become ignorant and not pursue the renewing of his mind. This is the most frequent ground given to evil spirits. But if there is only this kind of ground given, without the passivity spoken of below, the mind and memory will still not be weakened too severely.
All sins arise when one gives ground to evil spirits. When a believer pays attention to sin in his mind, it means he has loaned his mind to the evil spirits because all sins come from evil spirits. If a believer yields to sin in his mind, he cannot refuse the evil spirits behind the sin. However long sinful thoughts reside in the heart, the evil spirits will work within him. All filthy, haughty, unkind, unrighteous, and similar thoughts give ground to evil spirits. Believers who yield in their minds and do not refuse these kinds of thought will find these kinds of thought coming back more easily the next time. It also becomes harder to ward them off because evil spirits have already occupied a place in their minds.
In addition to sin, there are many other improper thoughts that can become a base of operation for evil spirits. Evil spirits often inject a thought into the believers. If they receive it, the thought becomes a ground for the evil spirits to work on. Every unconfirmed idea, every vain thought, every notion that comes from nowhere, a sentence one hears in passing, a line in a book one reads accidentally, as well as all the fancies in human life give ground to evil spirits. They enable the evil spirits to work in the future—perhaps after several years. They also cause the believers to be full of prejudice, rebel against God's truth, and believe in many heresies.