ROME, Italy — Pope Francis said in a letter published Tuesday that his lengthy illness has helped make “more lucid” to him the absurdity of war, as his top deputy shot down any suggestion of resignation and plans progressed for an April 8 meeting with Britain’s King Charles III.

Italian daily Corriere della Sera published a letter to the editor from Francis, signed and dated March 14 from Rome’s Gemelli hospital where the 88-year-old pontiff has been treated since Feb. 14 for a complex lung infection and double pneumonia.

In it, Francis renewed his call for diplomacy and international organizations to find a “new vitality and credibility.” And he said that his own illness had also helped make some things clearer to him, including the “absurdity of war.”

“Human fragility has the power to make us more lucid about what endures and what passes, what brings life and what kills,” he wrote.

Responding to a letter from the newspaper’s editor-in-chief, Luciano Fontana, Francis also urged him and all those in the media to “feel the full importance of words.”

“They are never just words: they are facts that shape human environments. They can connect or divide, serve the truth or use it for other ends,” he wrote. “We must disarm words, to disarm minds and disarm the Earth.”

The letter was published as Francis registered slight improvements in his treatment and as the Vatican No. 2, Cardinal Pietro Parolin, shot down any suggestion the pope might resign.

“Absolutely no,” Parolin told journalists on Monday. Parolin has visited Francis twice during his hospitalization, most recently March 2, and said he found Francis better then than his first visit Feb. 25.

Francis is now able to spend some time during the day off high flows of oxygen and use just ordinary supplemental oxygen delivered by a nasal tube, the Holy See press office said. Doctors are also trying to cut back on the amount of time he uses a noninvasive mechanical ventilation mask at night, to force his lungs to work more.

While those amount to “slight improvements,” the Vatican isn’t yet providing any timetable on when he might be released. That said, Buckingham Palace announced Monday that King Charles III was scheduled to meet with Francis on April 8 at the Vatican.

Such state visits are always closely organized with Parolin’s office, suggesting that the Holy See believed the pope would be back home by then, barring any setbacks.

The developments came as the Vatican released some details on the first photograph of Francis released since his hospitalization. The image, taken Sunday from behind, showed Francis sitting in his wheelchair in his private chapel in prayer without any sign of nasal tubes.

The photo, showing Francis wearing a Lenten purple stole, followed an audio message Francis recorded March 6 in which he thanked people for their prayers, his voice soft and labored.

Together, they suggested Francis is very much controlling how the public follows his illness to prevent it from turning into a spectacle. While many in the Vatican have held up St. John Paul II’s long and public battle with Parkinson’s disease and other ailments as a humble sign of his willingness to show his frailties, others criticized it as excessive and glorifying sickness.

The image certainly reassured some well-wishers who came to Gemelli to pray for Francis, who is recovering in the 10th floor papal suite reserved for popes.

“After a month of hospitalization, finally a photo that can assure us that his health conditions are better,” said the Rev. Enrico Antonio, a priest from Pescara.

At the Vatican, Sister Mary, a nun from Kenya, said she thought “he looks great.”

“The situation was very critical. But now seeing the photo, it makes me smile. It makes me feel better,” she said. “It makes me even feel safer that the church is still going on, that our pope can come back to us.”

But Benedetta Flagiello of Naples, who was visiting her sister who is a patient at Gemelli, wondered if the photo was even real.

“Because if the pope can sit for a moment without a mask, without anything, why didn’t he look out the window on the 10th floor to be seen by everyone?” she asked. “If you remember our old pope (John Paul II), he couldn’t speak up, but he showed up.”

Paolo Santalucia and Silvia Stellacci contributed.