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.