After a believer repents, his mind is not completely delivered from Satan’s workings. As Satan previously worked through the mind, he still works now through the mind. The apostle said to the believers in Corinth, "But I fear lest somehow, as the serpent deceived Eve by his craftiness, your thoughts would be corrupted from the simplicity and the purity toward Christ" (2 Cor. 11:3). The apostle knew how the god of this world had blinded the minds of the unbelievers and, in the same way, how he was deluding the minds of those who already had believed. The apostle knew that even though the believers were already saved, their minds were not yet renewed. Therefore, it remains the most critical battlefield—the mind receives more attacks from the authority of darkness than any other organ of man’s entire being. We must realize that evil spirits of Satan pay special attention to our minds and that they always attack us in our minds. "As the serpent deceived Eve by his craftiness." Satan did not attack Eve’s heart first, he attacked her mind first. In the same manner, evil spirits want to attack our mind first, not our heart, with the purpose of corrupting us from a faith in simplicity. They know that our mind is the weakest spot. Before we believed, the mind was their stronghold; even now there are still many places that are not yet overthrown. They start where they can be most successful. Eve’s heart was sinless, but she accepted the thought suggested by Satan in her mind. She was enchanted by the power of his subtlety to the point that her mind lost its rationality, thereby becoming trapped. Therefore, it is useless for a believer to boast that he is upright in his motive. His mind must be trained to withstand evil spirits. Otherwise, they will have a way to tempt and to deceive his mind, and will cause his will to lose its power of decision.
Following 2 Corinthians 11:3, the apostle tells us where this danger comes from. Some will preach "another Jesus," causing them to "receive a different spirit" and accept "a different gospel" (v. 4). This means that the danger to the believers is to have erroneous teachings instilled into their minds which will lead them away from the pure gospel of Christ. This is what the "serpent" wants to do today. Satan will pretend to be an angel of light so that in their minds, believers will worship "another Jesus" who is not the Lord, receive "a different spirit" which is not the Holy Spirit, and through the believers spread "a different gospel" which is not the gospel of God’s grace. The apostle told us that all this is done by Satan in the mind of the believers. One by one, Satan turns these "teachings" into thoughts and instills them into the mind of the believers. It is a very pitiful thing today that few believers are able to know these matters. How many believers know that Satan gives "good" thoughts to man?
We should know that a believer can receive a new life, a new heart, but not a new mind. Many believers have a new heart, but their head is old. The heart is full of love, but the head (the mind) does not have any discernment. Many are pure in their motive, but not so clear in the thoughts in their head. The mind is full of all kinds of mixture and very lacking in crucial, spiritual discernment. Many believers truly have a tender regard in their hearts for all of God’s children, yet their minds are full of ideals, opinions, and goals. Many of God’s best and most faithful children are very narrow and prejudiced in their thoughts. They have made up their minds about the truth. They only want their kind of truth and completely reject anything else which does not agree with their prejudices. All this happens because their heads are not as big as their hearts. There are also many of God’s children whose minds can never come up with anything. Although they have heard many truths, they can never remember them; neither can they put them into practice or spread them to others. They have heard plenty, but there is no strength to express what they have heard. Though they have been receiving truths for years, they cannot meet the smallest needs of others. This kind of people may even boast that they are full of the Holy Spirit! This happens because their minds have not been completely renewed.
(Spiritual Man, The (3 volume set), Chapter 31, by Watchman Nee)