The Latent Power of the Soul by Watchman Nee
From the back cover:
"The peril of the believer is to confuse the spirit for the soul and the soul for the spirit, and so be deceived into accepting the counterfeit of evil spirits to the unsettling of God's work. The greatest advantage in knowing the difference between spirit and soul is perceiving the latent power of the soul and in understanding its falsification of the power of the Holy Spirit. Such knowledge is not theoretical but practical in helping people to walk in God's way."
Watchman Nee: Nee Shu-tsu was born in 1903 into a Christian family in Foochow, China. At the age of 17, after considerable struggle, he found salvation, testifying “From the evening I was saved, I began to live a new life, for the life of the eternal God had entered into me.” Nee was exceptionally intelligent and devoted to studying Yah's word, receiving great revelations and strength from the Holy Spirit through his sufferings, and writing extensively about soul and spirit. He was imprisoned in China for his faith in 1952, and died while in confinement on May 30, 1972. The Latent Power of the Soul (1933) and The Release of the Spirit (1965) are two of his greatest accomplishments.