This entrance was both unexpected and welcome. The thunderous applause and cheers on Sunday made it clear as Pope Francis made his first public appearance since leaving a Rome hospital two weeks ago.

Francis arrived unannounced on the dais in St. Peter’s Square near the end of a Mass that was part of a pilgrimage by healthcare workers and their patients.

The pope spoke very few words, his voice still strained after a six-week hospital stay for pneumonia and other problems that his doctors said twice brought him close to death.

“Happy Sunday to everyone, many thanks,” Francis said, waving his hands. A nasal cannula was visible in both nostrils; Francis continues to rely on supplemental oxygen, the Vatican has said.

In a wheelchair pushed by his trusted nurse, Massimiliano Strappetti, Francis moved through groups of pilgrims — including dozens of doctors and nurses from around the world — who had come the Vatican on Sunday for this weekend’s Jubilee of the Sick and Health Care Workers.

“What a wonderful surprise — the pope still has health problems but he wanted to give a gift to the faithful,” said Lamberto Rosa, a businessman who volunteers with the Order of Malta at some Vatican events. “He has a fighting spirit and wants to be present.”

Francis has made physical closeness to his flock, dramatic gestures and a freewheeling style the hallmarks of his pontificate, and his appearance on Sunday suggested that he was determined to carry on with that approach despite his physical limitations.

Since leaving the hospital in March, he has been living in his suite on the second floor of the Vatican guesthouse he calls home. The Vatican press office has repeatedly said that Francis has not been receiving visitors as he convalesces, though it reported on Friday that his speech was improving.

“It must have cost him a lot to go through that,” said, Giuseppe Vanacore, the president of Italy’s national association for kidney transplant patients, who was present in the square on Sunday. Mr. Vanacore said he had been moved by the homily the pope had written for the Mass, which was read by Cardinal Rino Fisichella.

Before beginning, Cardinal Fisichella had told those present that Francis, like many ill people, was watching the Mass on television.

In the homily, Francis wrote that he had “much in common with you at this time of my life, dear brothers and sisters who are sick: the experience of illness, of weakness, of having to depend on others in so many things, and of needing their support.” That “is not always easy,” he wrote.

In his traditional Sunday blessing, made public after the Mass, Francis wrote that he prayed “for doctors, nurses and health workers,” who often worked in difficult conditions. “Their mission is not easy and must be supported and respected,” he said, adding that he hoped “necessary resources will be invested in treatment and research, so that health systems are inclusive and attentive to the most fragile and the poorest.”

After the Mass, the Vatican issued a statement saying that Francis had prayed and participated in the ritual of passing through the Holy Door in St. Peter’s Basilica, like other pilgrims.

On Friday, in its twice-weekly briefing on Francis’ health, the Vatican said the pope was “dedicating a lot of time to motor and respiratory therapy,” showing improvements in both. It added that the flows of supplemental oxygen he required were becoming less intense, and that blood tests showed that the infections in his lungs were also improving.

People applauded and cheered as Francis moved through the crowd on Sunday. Some pumped their fists in encouragement, others waved flags. “Long live the pope,” they cheered.

“It was a grand gesture — he showed his suffering,” said Massimiliano Porena, a nurse from San Camillo hospital in Rome. He described the appearance as “an act of love” toward health workers, “something we try to transmit to the patients we care for.”