I have always thought that doubt is a necessary element of faith, rather like darkness is a necessary complement to light--how do you know it's light unless there has been darkness? Similarly, how can you know you have faith unless you doubt and question?
The article on Mother Teresa's doubts in Time magazine, and the book of letters that prompted the article, Mother Teresa: Come Be My Light compiled by Rev. Brian Kolodiejchuk, which I have not yet read, give us a deep look into doubt, deeper than most of us are willing to acknowledge or speak. Based on the excerpts in Time, it is no wonder she wanted the letters destroyed. I hope to find time to read the book if only to see if it gives a clue about how she kept on going, doing the work she had been called to do, while being in such a state of doubt. Many others of us, when we doubt or question, just throw in the towel and think that it's not worth it--why didn't she?
In A Hidden Wholeness, Parker J. Palmer (p. 82-83) talks about the need to hold paradoxes as both-and, not either-or:
"Spring is the season of surprise when we realize once again that despite our perennial doubts, winter's darkness yields to light and winter's deaths give rise to new life. So one metaphor for spring is 'the flowering of paradox.' As spring's wonders arise from winter's hardships, we are invited to reflect on the many 'both-ands' we must hold to live life fully and well--and to become more confident that as creatures embedded in nature, we know in our bones how to hold them.
The deeper our faith, the more doubt we must endure; the deeper our hope, the more prone we are to despair; the deeper our love, the more pain its loss will bring: these are a few of the paradoxes we must hold as human beings. If we refuse to hold them in hopes of living without doubt, despair, and pain, we also find ourselves living without faith, hope, and love. But in the spring we are reminded that human nature, like nature herself, can hold opposites together as paradoxes, resulting in a more capacious and generous life."
I would guess that Palmer would suggest that Mother Teresa began with a very deep faith and had a long and excruciatingly difficult period of doubt as the paradox that she had to hold. May our own paradoxes be as fulfilling, so that despite the possibility of doubt, despair and pain, we can move toward faith, hope and love.