"Insanity and Spiritual Songs in the Soul of the Saint"
This was an interesting biography of William Cowper by Piper. Here is a small quote I liked:
"Periodic self-examination is needed and wise and Biblical. But for the most part mental health is the use of the mind to focus on worthy reality outside ourselves."
I think this hits on a very important element of depression.
"Fight the Good Fight of Faith"
An article by Terry Virgo.
"If you want success in your Christian life you are going to have to fight for it, but notice the sphere in which the battle rages. It is a fight not of willpower nor intellect nor emotion but a fight of faith!"