Spiritual Depression: Its Causes and Its Cure, Dr. Martyn Lloyd-Jones, 1965. Gently but firmly addresses potential causes including inability to receive forgiveness for all sins, not moving beyond past failures, seeing only bad and not good, not recognizing false teaching, lack of faith, not seeing trials correctly, etc. This older book stays centered on Biblical solutions. Very helpful.
Dagg Manual of Theology (and links to this work in various other formats).
Dagg Manual of Theology (MySword for Android)
Dagg Manual of Theology (theWord Bible Format)
Dagg Manual of Theology (esword format)
Dagg Manual of Theology (PDF Format)
