Jesus has a very special love for you. As for me, the silence and the emptiness is so great that I look and do not see, listen and do not hear.
— Mother Teresa to the Rev. Michael Van Der Peet, September 1979
To feel so much pain, and yet to give out so much light -- what better defines a saint, I say?
With the unearthing of her letters, there's a lot of discussion of why she did not feel the presence of God for the longest time, with discussions ranging from philosophical to theological, to psychological.
What about the merely practical? Try living your life in a slum, in all its misery, constant violence, filth, opportunism and hopelessness. Would your being not absorb all that and feel emptiness and pain?
Burnout, like some activists I know.
http://www.time.com/time/world/article/0,8599,1655415,00.html