(CBS) In life, Mother Teresa was an icon — for believers — of God’s work on Earth. Her ministry to the poor of Calcutta was a world-renowned symbol of religious compassion.

But now, it has emerged that Mother Teresa was so doubtful of her own faith that she feared being a hypocrite

In a new book that compiles letters she wrote to friends, superiors and confessors, her doubts are obvious.

According to her letters, Mother Teresa died with her doubts. She had even stopped praying, she once said.