Spiritual Causes of Depression

I believe that much of the causes of my personal depression are spiritual problems (self-pity, pride, worry, discouragement, lack of faith), but here is another helpful side to the discussion:

"Some who are depressed strongly react against the suggestion of a possible spiritual cause. Others race toward the idea; they hope that once they discover the core sin, everything will change. They feel as if they must be spiritually deficient because they have no joy, no deep affection, no spiritual vitality. Maybe, they think, they are among the "lukewarm" of the book of Revelation (Rev. 3:16), a group they rightly would like to leave as soon as possible. But depression is a time to revisit both our own expectations and God's for our emotional life. Contrary to what we might think, God says that strong faith can coexist with emotional highs, lows, and everything in between. It is a myth that faith is always smiling. The truth is that faith often feels like the very ordinary process of dragging one foot in front of the other because we are conscious of God." (Edward T. Welch, Depression a Stubborn Darkness, pg. 31)