A symbol of goodness for people everywhere, she was the recipient of many awards, including the 1979 Nobel Peace Prize. When she died on September 5, 1997, her congregation, the Missionaries of Charity, encompassed 594 homes in 123 countries. She left behind her more than 3,800 sisters, nearly 380 brothers, thirteen priests, and countless co-workers, all committed to living in her spirit throughout the world.

Hers is quite a success story, even though she insisted that she was called to be faithful, not successful. But for all her popularity and success, not many know about the way in which God formed her and prepared her for her calling.

Discerning Her Call. She was born Agnes Gonxha Bojaxhiu on August 26, 1910, the youngest of three children of Albanian parents. She grew up in the multiethnic, multifaith town of Skopje, where her father was a successful businessman. By her own account, her childhood was happy, and on the day of her First Holy Communion (at the age of five), she was graced with a “love of souls,” a gift from God that would come to characterize her whole life.

The sudden death of Agnes’ much-loved father in 1919 left the family financially insecure. But it also allowed Agnes’ faith to be fuelled by her devout mother and by priests at the local church. By the age of twelve, she felt called to be a missionary among the poor, but she was reluctant to leave her mother alone. In addition to this reluctance, she also had times of doubt: Was she really called to “belong completely to God”? A few years later, a Croatian priest introduced her to St. Ignatius Loyola’s Spiritual Exercises, in which she found the answer that she was looking for. The thought of mission work filled her with joy, despite the challenges and sufferings it entailed. And that joy was all the confirmation she needed.

Agnes’ eventual departure to become a Loreto Sister was nonetheless difficult. At the age of eighteen, when she told her mother, it was only after a delay that she received her blessing—along with the reminder that her daughter must now be “only all for God and Jesus.”

From Sister to Mother. When Agnes set sail for India in 1928, she had chosen Teresa as her religious name. She was at pains to emphasize that this was not after the great Teresa of Àvila but after Thérèse of Lisieux, “The Little Flower.” Agnes loved how Thérèse pointed the way to holiness through fidelity in small things and how she spoke of the immense power of suffering to win God’s grace for others. She was also touched by Thérèse’s desire to “love Jesus as he had never been loved before,” a reminder of the words Agnes’ mother used. But there must have been something prophetic in this choice of names as well, for just as Agnes would in her later years, Thérèse had experienced a spiritual darkness that she endured only through faith—a “blind” faith that offered no consolation.

For more than fifteen years, Sister Teresa taught history and geography in a responsible but unexceptional way. Her sisters in Loreto remembered her for her industriousness, her readiness to perform menial tasks, her ill-fitting sandals, and her fun-loving nature. But something else was going on inside her. In 1931, for example, she spent a little time helping out at a small medical station that served the suffering poor. Already by this time, she saw an intimate and mysterious relationship between them and the vulnerable Christ. In the hospital pharmacy, there hung a picture of Christ the Redeemer surrounded by a crowd of people on whose faces were engraved the torments of their lives. As she confronted the needs of the waiting throngs, Sister Teresa would look at that picture and think: “Jesus, it is for you and for souls!”

In 1937, shortly before making her final vows and becoming “Mother Teresa,” she wrote to her spiritual director of how she had joyfully carried the cross with Jesus. She told how crosses used to frighten her. But now, she embraced suffering, and because of this, “Jesus and I live in love.” The precise nature of these crosses, which had made her weep, remained unspecified. She may have been referring to her experience as an Albanian and being an outsider in Loreto life in India. But more profoundly, she referred to a “darkness” that was her companion: a darkness that would become the subject of a number of letters to successive spiritual directors and priests, published only after her death. These letters give the impression that Mother Teresa experienced both interior suffering and spiritual dryness, a feeling that God was absent despite her great thirst for him.

Refuse Him Nothing. Such was Mother Teresa’s love for God that in 1942, like Thérèse of Lisieux, she made a private vow never to refuse him anything. She was determined that this vow would touch every aspect of her life, that she would say yes to God in every circumstance, no matter how challenging or difficult it might be. This vow dealt not only with the heroic aspects of holiness but the everyday routines of life as well. In the spirit of St. Thérèse’s “Little Way,” she promised to do small things with great love. Every action, every sacrifice, was to be motivated by love.

On September 10, 1946, on a train to Darjeeling and in the course of a subsequent retreat, Mother Teresa had a powerful experience of the Lord in which he asked her to leave Loreto and found a new congregation in Calcutta dedicated to the “wholehearted free service of the poorest of the poor.” The goal of this congregation would be to meet Jesus’ thirst for souls as he hung on the cross. Remembering her vow, Mother Teresa knew that she could not refuse him. Jesus’ thirst—his longing for the love of the broken bodies of the poor and his desire to offer himself as spiritual drink to these poor—was at the heart of all that followed. Jesus wanted their love, and he wanted to give himself to them so that they would be free to give themselves back to him.

But before she could step out in faith to fulfill this vision, she had to convince her spiritual director and her religious superiors that this “second calling” was indeed valid. Loreto had taught her obedience, but for a while, their directions to wait appeared to be in direct conflict with God’s will. She insisted on the need to respond swiftly, but in obedience she submitted to the Church’s directives, painful though it was. Finally, in April 1948, Rome granted her an “indult of exclaustration,” allowing her to start life in the slums while still remaining a religious sister.

Leaving Loreto was the hardest thing Mother Teresa had to do. She was stepping out into one of the darkest, most disease-ridden areas of the world. And she was going there alone. She was aware of her inadequacy and the delicacy of her situation as a solitary woman. The Loreto order was highly regarded in Calcutta. Could abandoning it really be God’s will? Some even condemned the move as a wile of the devil. But she was determined to deny Jesus nothing, not even the suffering that came from gossip, misunderstanding, and isolation.

A Life Filled with Joy. The work began with a tiny school where Mother Teresa taught her “students” by scratching the alphabet in the dust and introducing them to the rudiments of hygiene. Tortured with fear and loneliness and not very good at begging, she was painfully aware of the need for prayerful support. Gradually some of her former pupils joined her, and in 1950 her new congregation was formally established. In 1952, she wrote to a friend in Belgium, whose ill health prevented her from joining the congregation, and asked her to offer her suffering to the Lord as a form of intercession for Mother Teresa’s work. And thus began the “Sick and Suffering Co-Workers,” whose numbers continued to grow alongside the Missionaries of Charity.

It wasn’t just religious sisters who joined her either. Laypeople came, and she eventually founded a lay branch of her congregation, as well as an order of priests. She opened soup kitchens, children’s homes, homes for the dying, leprosy clinics, and homes for AIDS victims. A prayerful woman whose outreach was fueled by contemplation, she was constantly uncomfortable with her growing popularity, especially with the increased requests for her to speak at conferences and gatherings all over the world. But again, she did not refuse the Lord, no matter how much it cost her.

While the world acclaimed her, Mother Teresa came to see this very world, not just the world of the poor, but the world of the middle class and the world of the well-off, as an open Calvary. Her travels to wealthier countries convinced her that spiritual poverty was a bigger problem than the physical poverty of the “Third World” in which she worked. Faithful to the last in her determination to love God as he had never been loved before, and in spite of the physical hardships and spiritual suffering she endured, Mother Teresa’s life was filled with joy. Why? Because she always found Jesus in the poor. Because every act of love brought her “face to face with God.”

Kathryn Spink is the author of Mother Teresa: A Complete Authorized Biography (Harper One).