For suffering Christians, the book "Be Still, My Soul: Embracing God's Purpose and Provision in Suffering; 25 Classic and Contemporary Readings on the Problem of Pain", edited by Nancy Guthrie, is a must to own.
Here's just a little taste of the wealth of encouragement (which ranges as far back as St. Augustine and moves to the present day writings of the likes of John Piper and Joni Eareckson Tada):
"Strange as it may sound, it is yet true that much of the suffering we are called upon to endure on the highway of holiness is an inward suffering for which scarcely an external cause can be found. For our journey is an inward journey, and our real foes are invisible to the eyes of men.
Attacks of darkness, of despondency, of acute self-depreciation may be endured without any change in our outward circumstances. Only the enemy and God and the hard-pressed Christian know what has taken place.
The inward suffering has been great and a mighty work of purification has been accomplished, but the heart knoweth its own sorrow and no one else can share it. God has cleansed his child in the only way he can, circumstances being what they are.
Thank God for the furnace."
A.W. Tozer (1897-1963)