What is the nature of man?

The heart of man is the inner man and the place where thinking takes place. Without faith, the mind is under the dictates of the sin nature and is absolutely untrustworthy. It is described as deceitful, fraudulent, and polluted (Jer. 17:9–10). The heart of man is incurable and malignant. No one can understand the heart except God, and without the illuminating, teaching, and convicting ministries of the Holy Spirit, humans cannot understand who they are or why they do the things they do (Jer. 17:9–10; 1 Cor. 2:9–11). The struggle for spiritual power is a battle between two opposing forces: the flesh (sin nature) and the Spirit of God. As believers, we are born again into this world as frontline fighters in a universal conflict against Satan and his angels (Rev. 12:3, 4, 7). Our old man (life under the dominion of sin) was crucified with Christ, but the sin nature is still present and will fight the work of the Spirit at every step (Rom. 6:6). We are a three-part being of spirit, soul, and body, and between our human spirit (where the Holy Spirit dwells) and the flesh (where the sin nature dwells) is the battlefield of the soul (1 Thess. 5:23). Our freedom in Christ involves a choice to serve either sin or the Spirit (Gal. 5:17).