The knowledge most lacking among believers today concerns the existence of the human spirit and its function. Many believers do not know they have a spirit in addition to their mind, emotion, and will. Even after hearing that there is a spirit within man, they either think that their mind, emotion, or will is the spirit, or they are puzzled and do not know where their spirit is. This ignorance is a very serious matter. Because of this, believers do not know how to cooperate with God, control themselves, and fight against Satan, since all these three things require the work of the spirit. The most important thing that a believer should know is that there is a spirit within him besides the thought, knowledge, and imagination of the mind; the feeling, love, and desire of the emotion; and the ideas, opinion, and determination of the will. The spirit is deeper than the mind, emotion, and will. A believer should know that he has a spirit; he also should know the feeling of the spirit, its working, its power, and the principle of its activity. Only in this way will a believer be able to know how to walk according to the spirit, not according to the fleshly soul or body.