Generally speaking, before a believer has experienced the baptism of the Holy Spirit, he is like the servant of Elisha, who was very unclear about the realities in the spiritual realm (2 Kings 6:15-17). Although he may have received the teachings of the Bible and some instructions, he only understands them according to his mind and has no revelation in his spirit. The intuition in his spirit becomes quite keen only after he has experienced the baptism of the Holy Spirit. In his spirit, a whole spiritual world will be opened up before him. When a believer passes through the baptism of the Holy Spirit, he comes in contact with God’s supernatural power and touches a personal God.
At this point real spiritual warfare begins. First, the power of darkness will disguise itself as an angel of light and imitate the person and work of the Holy Spirit. Second, the intuition in the spirit will become truly aware of the existence of the spiritual realm and will know the reality of Satan and the evil spirits. The apostles did not receive the expounding of the Scripture by the Lord until after Golgotha. They saw the reality of the spiritual realm only after Pentecost. The baptism of the Spirit is the beginning of spiritual warfare.
After a believer has experienced the baptism of the Holy Spirit and comes in contact with a personal God, after his spirit is released and freed, and he realizes the reality of matters in the spiritual realm, he will engage Satan in warfare if he has the knowledge. (We should remember that although a spiritual man has knowledge, his knowledge does not come all at once, but is acquired through many testings.) Only a spiritual man knows the reality of the spiritual enemy, and only he will fight with such an enemy (Eph. 6:12). This warfare is not with fleshly weapons (2 Cor. 10:3-4). Since the warfare is spiritual, the weapons must also be spiritual. Hence, this kind of warfare is a warfare between man’s spirit and the enemy’s spirit. This is the warfare of spirit with spirit.
If a believer has not reached this spiritual state, he will neither understand nor be able to engage in such a warfare in the spirit. He understands the way to "wrestle" with the enemy with his spirit only when the Holy Spirit strengthens the power of his spirit. Believers see the reality of Satan and his kingdom and then know how to withstand and attack him with their spirit only when they become spiritual.
There are many reasons for such warfare. The greatest reason is the enemy’s attack and obstruction. Satan always applies his tactics to assault spiritual believers. Sometimes he assaults the emotion. At other times he assaults the body. There are also many obstacles that he places in the believers’ work and environment. Another reason for spiritual warfare is to fight for God. Satan has countless works in this world and has designed countless schemes in the air. His works and schemes are all for the purpose of opposing God. When we are for God, we fight against Satan with our spiritual strength, destroy his schemes, and work with the words of our prayer. Although at times we do not know what he is scheming or doing, we fight against him anyway because he is always our enemy.
(Spiritual Man, The (3 volume set), Chapter 18, by Watchman Nee)