On 10 September 1946, Teresa experienced what she later described as "the call within the call" while traveling by train to the Loreto convent in Darjeeling from Calcutta for her annual retreat. "I was to leave the convent and help the poor while living among them. It was an order. To fail would have been to break the faith."
She began her missionary work with the poor in 1948, replacing her traditional Loreto habit with a simple white cotton sari decorated with a blue border. Mother Teresa adopted Indian citizenship, spent a few months in Patna to receive a basic medical training in the Holy Family Hospital and then ventured out into the slums. Initially she started a school in Motijhil (Calcutta); soon she started tending to the needs of the destitute and starving. In the beginning of 1949 she was joined in her effort by a group of young women and laid the foundations to create a new religious community helping the "poorest among the poor".
Her efforts quickly caught the attention of Indian officials, including the prime minister, who expressed his appreciation.
Teresa wrote in her diary that her first year was fraught with difficulties. She had no income and had to resort to begging for food and supplies. Teresa experienced doubt, loneliness and the temptation to return to the comfort of convent life during these early months.
She wrote in her diary:
Our Lord wants me to be a free nun covered with the poverty of the cross. Today I learned a good lesson. The poverty of the poor must be so hard for them. While looking for a home I walked and walked till my arms and legs ached. I thought how much they must ache in body and soul, looking for a home, food and health. Then the comfort of Loreto [her former order] came to tempt me. 'You have only to say the word and all that will be yours again,' the Tempter kept on saying ... Of free choice, my God, and out of love for you, I desire to remain and do whatever be your Holy will in my regard. I did not let a single tear come.
Teresa received Vatican permission on 7 October 1950 to start the diocesan congregation that would become the Missionaries of Charity. Its mission was to care for, in her own words, "the hungry, the naked, the homeless, the crippled, the blind, the lepers, all those people who feel unwanted, unloved, uncared for throughout society, people that have become a burden to the society and are shunned by everyone."
It began as a small order with 13 members in Calcutta; today it has more than 4,000 nuns running orphanages, AIDS hospices and charity centers worldwide, and caring for refugees, the blind, disabled, aged, alcoholics, the poor and homeless, and victims of floods, epidemics, and famine.
In 1952 Mother Teresa opened the first Home for the Dying in space made available by the city of Calcutta. With the help of Indian officials she converted an abandoned Hindu temple into the Kalighat Home for the Dying, a free hospice for the poor. She renamed it Kalighat, the Home of the Pure Heart (Nirmal Hriday). Those brought to the home received medical attention and were afforded the opportunity to die with dignity, according to the rituals of their faith; Muslims were read the Quran, Hindus received water from the Ganges, and Catholics received the Last Rites. "A beautiful death," she said, "is for people who lived like animals to die like angels—loved and wanted."
Mother Teresa soon opened a home for those suffering from Hansen's disease, commonly known as leprosy, and called the hospice Shanti Nagar (City of Peace). The Missionaries of Charity also established several leprosy outreach clinics throughout Calcutta, providing medication, bandages and food.
As the Missionaries of Charity took in increasing numbers of lost children, Mother Teresa felt the need to create a home for them. In 1955 she opened the Nirmala Shishu Bhavan, the Children's Home of the Immaculate Heart, as a haven for orphans and homeless youth.
The order soon began to attract both recruits and charitable donations, and by the 1960s had opened hospices, orphanages and leper houses all over India. Mother Teresa then expanded the order throughout the globe. Its first house outside India opened in Venezuela in 1965 with five sisters. Others followed in Rome, Tanzania, and Austria in 1968; during the 1970s the order opened houses and foundations in dozens of countries in Asia, Africa, Europe and the United States.
The Missionaries of Charity Brothers was founded in 1963, and a contemplative branch of the Sisters followed in 1976. Lay Catholics and non-Catholics were enrolled in the Co-Workers of Mother Teresa, the Sick and Suffering Co-Workers, and the Lay Missionaries of Charity. In answer to the requests of many priests, in 1981 Mother Teresa also began the Corpus Christi Movement for Priests, and in 1984 founded with Fr. Joseph Langford the Missionaries of Charity Fathers to combine the vocational aims of the Missionaries of Charity with the resources of the ministerial priesthood. By 2007 the Missionaries of Charity numbered approximately 450 brothers and 5,000 nuns worldwide, operating 600 missions, schools and shelters in 120 countries.
Mother Teresa's philosophy and implementation have faced some criticism. Catholic newspaper editor David Scott wrote that Mother Teresa limited herself to keeping people alive rather than tackling poverty itself.
She has also been criticized for her view on suffering. She felt that suffering would bring people closer to Jesus. Sanal Edamaruku, President of Rationalist International , criticised the failure to give pain killers, writing that in her Homes for the Dying, one could “hear the screams of people having maggots tweezered from their open wounds without pain relief. On principle, strong painkillers are even in hard cases not given. According to Mother Teresa's bizarre philosophy, it is ‘the most beautiful gift for a person that he can participate in the sufferings of Christ’.”
The quality of care offered to terminally ill patients in the Homes for the Dying has been criticized in the medical press. The Lancet and the British Medical Journal reported the reuse of hypodermic needles, poor living conditions, including the use of cold baths for all patients, and an approach to illness and suffering that precluded the use of many elements of modern medical care, such as systematic diagnosis. Dr. Robin Fox, editor of The Lancet, described the medical care as "haphazard", as volunteers without medical knowledge had to take decisions about patient care, because of the lack of doctors. He observed that her order did not distinguish between curable and incurable patients, so that people who could otherwise survive would be at risk of dying from infections and lack of treatment.
Colette Livermore, a former Missionary of Charity, describes her reasons for leaving the order in her book Hope Endures: Leaving Mother Teresa, Losing Faith, and Searching for Meaning. Livermore found what she called Mother Teresa's "theology of suffering" to be flawed, despite being a good and courageous person. Though Mother Teresa instructed her followers on the importance of spreading the Gospel through actions rather than theological lessons, Livermore could not reconcile this with some of the practices of the organization. Examples she gives include unnecessarily refusing to help the needy when they approached the nuns at the wrong time according to the prescribed schedule, discouraging nuns from seeking medical training to deal with the illnesses they encountered (with the justification that God empowers the weak and ignorant), and imposition of "unjust" punishments, such as being transferred away from friends. Livermore says that the Missionaries of Charity "infantilized" its nuns by prohibiting the reading of secular books and newspapers, and emphasizing obedience over independent thinking and problem-solving.
