VATICAN CITY — She was known throughout the world as Mother Teresa, considered a saint by many for her charitable work among the poorest of the world’s poor. On Sunday morning, Pope Francis officially bestowed that title at her canonization ceremony in St. Peter’s Square.

“I think, perhaps, we may have some difficulty in calling her St. Teresa: Her holiness is so near to us, so tender and so fruitful, that we continue to spontaneously call her Mother Teresa,” the pope said in off-the-cuff remarks during his homily.

It was a festive atmosphere at the Vatican, under a broiling summer sun, and several flags fluttered in the light breeze: from Albania, representing the Roman Catholic nun’s ethnic origins; from Macedonia, to note her birthplace, Skopje; from India, where she spent most of her life, working in the slums of Kolkata; and from the many other countries where her humility and selflessness touched countless lives.

When Francis proclaimed her St. Teresa at the end of the formal ceremony, in Latin, the crowd erupted in sustained applause.