The difference between the doubt of a modern atheist and spiritual darkness is as distinct as the difference between a "Dear John" note and an "I miss you, Johnny" letter. These saints never cease having a relationship with God; on the contrary, their relationship grows more intense as they long to be reunited. They live the experience the Song of Solomon refers to: “I sought him whom my heart loves — I sought him but I did not find him..."
The dark night lasted as long as a year or two for Teresa [of Avila] and Thérèse [de Lisieux]. For Mother Teresa, it lasted 50 years. "Mother was sharing in the longing and sufferings of her beloved," said the postulator of her cause.
And far from masking this aspect of her faith life, as the article suggests she did, Mother Teresa put the insights she gained from it at the center of her congregation’s spirituality. Missionaries of Charity chapels are adorned with only a crucifix and the words "I thirst" over the tabernacle.
"This seems to me the most heroic thing of her spiritual life," said the priest. "Mother was not only sharing in the physical poverty of the poor, but also the sufferings of Jesus — his longing for union, as expressed in Gethsemane and on the cross."
Her unique experiences are what make Mother Teresa such a powerful intercessor for the Church of the 21st century.
There is much more fascinating comment in this article, and in the others referenced in Deirdre Good's blog. You need to read these comments for yourself; but before you do, read the long Time Magazine article they mostly refer to - from start to finish. So far from being the attack on Mother Teresa some of them unfairly imply, it is a superbly balanced account, ending with these words:
The particularly holy are no less prone than the rest of us to misjudge the workings of history - or, if you will, of God's providence. Teresa considered the perceived absence of God in her life as her most shameful secret but eventually learned that it could be seen as a gift abetting her calling. If her worries about publicizing it also turn out to be misplaced - if a book of hasty, troubled notes turns out to ease the spiritual road of thousands of fellow believers, there would be no shame in having been wrong - but happily, even wonderfully wrong - twice.