ROME — Capping a process that stretched on for almost 20 years, Pope Francis on Sunday formally declared Mother Teresa, the “nun of the gutters” who was a champion for the poor, the dying and the unborn, the newest saint of the Catholic Church.

Pope Francis, however, acknowledged the obvious on Sunday, saying that despite the fact she now has a formal title as St. Teresa of Calcutta, to the world she’ll always remain “Mother Teresa.”

In an indication that the spirit of service of the poor associated with this five-foot tall giant is also a hallmark of Francis’ papacy, the pontiff chose to mark the occasion by putting together a celebratory lunch for 1,500 homeless people from all over Italy.

That collection of poor and homeless, most of whom live or are taken care of by the Missionaries of Charity, the religious order founded by Mother Teresa of Calcutta, were also given VIP tickets for the Mass Francis celebrated on Sunday in a packed St. Peter’s Square.

During his homily, Pope Francis praised Mother Teresa as an “emblematic figure of womanhood” and “a tireless worker of mercy.”

He also underlined not only her love for the poor, but particularly that of the unborn: “In all aspects of her life, [Mother Teresa] was a generous dispenser of divine mercy, making herself available for everyone through her welcome and defense of human life, those unborn and those abandoned and discarded.”

The pontiff also described her commitment to defending life, “ceaselessly proclaiming that ‘the unborn are the weakest, the smallest, the most vulnerable.’”

According to Francis, Mother Teresa — the only Catholic saint to ever win a Nobel Prize back in 1979 — made her voice heard by the powers of this world, “so that they might recognize their guilt for the crime of poverty they created.”

“For Mother Teresa, mercy was the ‘salt’ which gave flavor to her work, it was the ‘light’ which shone in the darkness of the many who no longer had tears to shed for their poverty and suffering,” the pope said.

The feast for Catholicism’s latest saint will be marked every Sept. 5, the day of her death in 1997.

Tying Sunday’s celebration to the Holy Year of Mercy, which on this weekend also marked the jubilee of volunteers, Francis described Mother Teresa as a model of holiness.

“May this tireless worker of mercy help us to increasingly understand that our only criterion for action is gratuitous love, free from every ideology and all obligations, offered freely to everyone without distinction of language, culture, race or religion,” he said.

Addressing the volunteers and workers of mercy, Francis told them that “following Jesus is a serious task” yet “filled with joy” because it takes courage to recognize God in the poorest of the poor. To be able to do so, he said, volunteers who “out of love of Jesus serve the poor and the needy” should not expect a thank you, but “renounce all this because they have discovered true love.”

Although the crowd for the Mass is being estimated at more than 100,000 with a packed St. Peter’s Square, its size was significantly smaller than that of her beatification, back in 2003, when the crowds reached the end of Via della Conciliazione, the big avenue leading to the Vatican.

There are several possible reasons, one of them being that this is the last weekend of summer break in Italy, so the city of Rome is virtually empty apart from tourists and pilgrims.

A second possible reason is the fact that back in 2003, the beatification, considered the last step before sainthood, came on the heels of the 50th anniversary of the priestly ordination of St. John Paul II, which gathered hundreds of thousands in Rome, basically turning the two celebrations into one.

When the canonization rite and Mass were over, some 1,500 poor and needy people were directed towards the atrium of the Paul VI Hall, where the weekly general papal audiences are sometimes held during the worst periods of winter.

According to a Vatican statement, the needy came to Rome in buses from all over Italy, travelling during the night, to attend both the celebration and the lunch, which consisted of the world-famous Italian pizza, offered by a pizzeria from Naples. The lunch was served by some 250 Missionaries of Charity sisters and 50 members of the male branch.

“There is no alternative to charity,” Francis said on Sunday. “Those who put themselves at the service of others, even when they don’t know it, are those who love God.”