VATICAN CITY — Elevating the “saint of the gutters” to one of the Catholic Church's highest honors, Pope Francis on Sunday praised Mother Teresa for her radical dedication to society's outcasts and her courage in shaming world leaders for the “crimes of poverty they themselves created.”

An estimated 120,000 people filled St. Peter's Square for the canonization ceremony, less than half the number who turned out for her 2003 beatification. It was nevertheless the highlight of Francis' Holy Year of Mercy and possibly one of the defining moments of his mercy-focused papacy.

Francis has been dedicated to ministering to society's most marginal, from prostitutes to prisoners, refugees to the homeless. In that way, while the canonization of “St. Teresa of Kolkata” was a celebration of her life and work, it was also something of an affirmation of Francis' own papal priorities, which have earned him praise and criticism alike.

“Let us carry her smile in our hearts and give it to those whom we meet along our journey, especially those who suffer,” Francis said in his homily.

Born Agnes Gonxhe Bojaxhiu on Aug. 26, 1910, Teresa went to India in 1929 as a sister of the Loreto order. In 1946, she received what she described as a “call within a call” to found a new order dedicated to caring for the most unloved and unwanted, the “poorest of the poor” in the slums of her adopted city, Kolkata.

The Missionaries of Charity order went on to become one of the most well-known in the world, with more than 4,000 sisters in their trademark blue-trimmed white saris doing as Teresa instructed: “small things with great love.”

At the order's Mother House in Kolkata, hundreds of people watched the Mass on TV and clapped with joy when Francis declared her a saint.

They gathered around Teresa's tomb, which was decorated with flowers, a single candle and a photo of the saint.

“I am so proud to be from Kolkata,” said Sanjay Sarkar, a high school student on hand for the celebration. “Mother Teresa belonged to Kolkata, and she has been declared a saint.”

For Francis, Teresa put into action his ideal of the church as a “field hospital” for those suffering both material and spiritual poverty, living on the physical and existential peripheries of society.

In his homily, Francis praised her as the merciful saint who defended the lives of the unborn, sick and abandoned, recalling her strong opposition to abortion, which often put her at odds with progressives around the world.

“She bowed down before those who were spent, left to die on the side of the road, seeing in them their God-given dignity,” he said.

Teresa's most famous critic, Christopher Hitchens, has accused her of taking donations from dictators — charges church authorities deny. Francis chose to emphasize her other dealings with the powerful. “She made her voice heard before the powers of the world, so that they might recognize their guilt for the crimes of poverty they themselves created,” he said, repeating for emphasis “the crimes of poverty.”

Hundreds of Missionaries of Charity sisters had front-row seats at the Mass, alongside 1,500 homeless people and 13 heads of state or government and even royalty: Queen Sofia of Spain. For the homeless, Francis offered a luncheon afterward in the Vatican auditorium, catered by a Neapolitan pizza maker who brought his own ovens for the event.

The low turnout suggested that financial belt-tightening and security fears in the wake of Islamic extremist attacks in Europe may have kept pilgrims away.

Those fears prompted a huge, 3,000-strong law enforcement presence to secure the area around the Vatican and close the airspace above. Many of those security measures have been in place for the duration of the Jubilee year, which officially ends in November.

While Francis is clearly keen to hold Teresa up as a model for her joyful dedication to the poor, he was also recognizing holiness in a nun who lived most of her adult life in spiritual agony, sensing that God had abandoned her.

According to correspondence that came to light after she died in 1997, Teresa experienced what the church calls a “dark night of the soul” — a period of spiritual doubt, despair and loneliness that many of the great mystics experienced. In Teresa's case, it lasted for nearly 50 years — an almost unheard of trial.

She was awarded the Nobel Peace Prize in 1979 and died in 1997. Soon thereafter, Pope John Paul II placed her on the fast-track for sainthood.

Francis has confessed that he was somewhat intimidated by Teresa, knowing well she was as tough as she was tender. He quipped during a 2014 visit to Albania that he would never have wanted her as his superior because she was so firm with her sisters.

But on Sunday, he admitted that even he would find it hard to call her “St. Teresa,” since her tenderness was so maternal.

“Spontaneously, we will continue to say ‘Mother Teresa,'?” he said to applause.