KOLKATA, India Letters written by Mother Teresa which reveal she sometimes doubted God surprised and then inspired many among her order, her successor said ahead of Wednesday's 10th anniversary of the ethnic Albanian nun's death.
"The sisters were surprised, I was surprised to learn how she suffered in her thirst for God," said Sister Nirmala, the diminutive superior general of the Missionaries of Charity.
"She suffered, yet she had a mask on herself of mysterious joy which comes only from complete surrender to God."
Sister Nirmala succeeded an ailing Mother Teresa six months before she died aged 87 on September 5, 1997, and will help lead a special mass to mark her passing.
The collection of letters written to colleagues and superiors over 66 years and complied by an advocate for her sainthood are due to be published on Tuesday under the title "Mother Teresa: Come Be My Light".
They cover a range of subjects dear to the Roman Catholic nun but it is those which portray her as at times deeply tormented about her faith that have grabbed attention.
In 1956, the 1979 Nobel Peace Prize winner, who dedicated her life to the poor, sick and dying in India, wrote:
"Such deep longing for God -- and ... repulsed -- empty -- no faith -- no love -- no zeal."
After Time magazine published excerpts of the book on its Web site last month, Sister Nirmala said dozens of nuns had approached her asking what the letters meant.
"They understood that even as thoughts of God forsaking her entered her mind, she never rejected God, such was her thirst for God, such was her greatness," Sister Nirmala told Reuters at the weekend.
"Her letters are inspiring and it has inspired us more to carry on the good work."
In overcrowded India and elsewhere, Mother Teresa faced some strong criticism over what many saw as her dangerous opposition to population control, and stand against abortion.
Homes run by her order were also accused of doing little to alleviate the suffering of patients.
Meanwhile, Kolkata -- previously known as Calcutta and where Mother Teresa worked for decades among the poor and dying -- was painted as a pit of misery and suffering, critics argued, ignoring its long history of intellectual and artistic creativity.
But many others see her lifetime's work on behalf of the city's underclass, which thrust her to worldwide prominence, in a different light.
In the run up to Wednesday's anniversary, hundreds of people, both rich and the poor, have been thronging Mother House, the order's headquarters in Kolkata, to offer prayers and sing hymns.
There had been speculation the publication of the letters would hurt the procedure to make her a saint, but this weekend Pope Benedict said in a speech Mother Teresa's torment over God's silence was not unusual.
Mother Teresa was beatified in 2003 but has not yet been canonised by the Vatican.